100 Matching Results

Search Results

Advanced search parameters have been applied.

Glass particles produced by laser ablation for ICP-MSmeasurements

Description: Pulsed laser ablation (266nm) was used to generate glass particles from two sets of standard reference materials using femtosecond (150fs) and nanosecond (4ns) laser pulses with identical fluences of 50 J cm{sup -2}. Scanning electron microscopy (SEM) images of the collected particles revealed that there are more and larger agglomerations of particles produced by nanosecond laser ablation. In contrast to the earlier findings for metal alloy samples, no correlation between the concentration of major elements and the median particle size was found. When the current data on glass were compared with the metal alloy data, there were clear differences in terms of particle size, crater depth, heat affected zone, and ICP-MS response. For example, glass particles were larger than metal alloy particles, the craters in glass were less deep than craters in metal alloys, and damage to the sample was less pronounced in glass compared to metal alloys samples. The femtosecond laser generated more intense ICP-MS signals compared to nanosecond laser ablation for both types of samples, although glass sample behavior was more similar between ns and fs-laser ablation than for metals alloys.
Date: June 1, 2007
Creator: Gonzalez, J.; Liu, C.; Wen, S.; Mao, X. & Russo, R.E.
Partner: UNT Libraries Government Documents Department

Modeling phase transformation behavior during thermal cycling in the heat-affected zone of stainless steel welds

Description: An implicit finite-difference analysis was used to model the diffusion-controlled transformation behavior in a ternary system. The present analysis extends earlier work by examining the transformation behavior under the influence of multiple thermal cycles. The analysis was applied to the Fe-Cr-Ni ternary system to simulate the microstructural development in austenitic stainless steel welds. The ferrite-to-austenite transformation was studied in an effort to model the response of the heat-affected zone to multiple thermal cycles experienced during multipass welding. Results show that under some conditions, a transformation ``inertia`` exists that delays the system`s response when changing from cooling to heating. Conditions under which this ``inertia`` is most influential were examined. It was also found that under some conditions, the transformation behavior does not follow the equilibrium behavior as a function of temperature. Results also provide some insight into effect of composition distribution on transformation behavior.
Date: December 31, 1995
Creator: Vitek, J.M.; Iskander, Y.S. & David, S.A.
Partner: UNT Libraries Government Documents Department

Stressed Heat Affected Zone Simulations of AerMet 100 Alloy

Description: AerMet 100 is a high strength, high fracture toughness alloy designed for use in aerospace applications. In previous work the welding behavior of this alloy has been evaluated, and it has been shown that a softened region in the heat-affected zone (HAZ) is a principal feature of the weld zone. A model for this softening, based on classical theories of precipitate coarsening and isothermal softening data, was developed and found to provide a reasonable description for weld thermal cycle simulation (Gleeble) experiments. Recent work has shown, however, that softening in real welds is not always well predicted by this model, so that additional effects, which are not captured in conventional Gleeble thermal cycle simulations must be addressed. In particular, the stresses associated with real weld HAZ's may modify the softening kinetics. In the current work, Gleeble simulations in both stress-free and stressed conditions have been conducted and the kinetics compared. The accuracy of the thermal model predictions have also been considered regarding their impact on estimated hardness values.
Date: August 3, 1999
Creator: Puskar, Joseph D. & Smith, Mark F.
Partner: UNT Libraries Government Documents Department

Development of the Cylindrical Wire Electrical Discharge Machining Process.

Description: Results of applying the wire Electrical Discharge Machining (EDM) process to generate precise cylindrical forms on hard, difficult-to-machine materials are presented. A precise, flexible, and corrosion-resistant underwater rotary spindle was designed and added to a conventional two-axis wire EDM machine to enable the generation of free-form cylindrical geometries. A detailed spindle error analysis identifies the major source of error at different frequency. The mathematical model for the material removal of cylindrical wire EDM process is derived. Experiments were conducted to explore the maximum material removal rate for cylindrical and 2D wire EDM of carbide and brass work-materials. Compared to the 2D wire EDM, higher maximum material removal rates may be achieved in the cylindrical wire EDM. This study also investigates the surface integrity and roundness of parts created by the cylindrical wire EDM process. For carbide parts, an arithmetic average surface roughness and roundness as low as 0.68 and 1.7 {micro}m, respectively, can be achieved. Surfaces of the cylindrical EDM parts were examined using Scanning Electron Microscopy (SEM) to identify the craters, sub-surface recast layers and heat-affected zones under various process parameters. This study has demonstrated that the cylindrical wire EDM process parameters can be adjusted to achieve either high material removal rate or good surface integrity.
Date: January 22, 2002
Creator: McSpadden, SB
Partner: UNT Libraries Government Documents Department

Transverse texture and microstructure gradients in friction-stir welded 2519 aluminum.

Description: Friction-stir welding produces severe thermomechanical transients that generate crystallographic texture evolution throughout the weld-affected microstructure . In this study, a friction stir weld in a coarse-grained 2519 aluminum plate was investigated in order to resolve the influence of these thermal and deformation effects on texture and microstructure development . Automated electron backscatter diffraction (EBSD) was applied to spatially resolve orientations in the base metal, weld nugget, and thermomechanical and heat-affected zones. Results show a gradient demarcated by an alteration in boundary character, texture, and precipitate distribution between the thermomechanical affected zone and the recrystallized weld nugget . EBSD scans and microstructural characterizations reveal substructure evolution from the base plate to the nugget indicative of dynamic recovery and recrystallization processes . Experimental results of texture evolution, however, did not directly follow from considerations of simplified deformation gradients and resultant simple shear textures resulting from restricted glide .
Date: January 1, 2003
Creator: Bingert, J. F. (John F.) & Fonda, R. W. (Richard W.)
Partner: UNT Libraries Government Documents Department

STRESS CORROSION CRACKING IN TEAR DROP SPECIMENS

Description: Laboratory tests were conducted to investigate the stress corrosion cracking (SCC) of 304L stainless steel used to construct the containment vessels for the storage of plutonium-bearing materials. The tear drop corrosion specimens each with an autogenous weld in the center were placed in contact with moist plutonium oxide and chloride salt mixtures. Cracking was found in two of the specimens in the heat affected zone (HAZ) at the apex area. Finite element analysis was performed to simulate the specimen fabrication for determining the internal stress which caused SCC to occur. It was found that the tensile stress at the crack initiation site was about 30% lower than the highest stress which had been shifted to the shoulders of the specimen due to the specimen fabrication process. This finding appears to indicate that the SCC initiation took place in favor of the possibly weaker weld/base metal interface at a sufficiently high level of background stress. The base material, even subject to a higher tensile stress, was not cracked. The relieving of tensile stress due to SCC initiation and growth in the HAZ and the weld might have foreclosed the potential for cracking at the specimen shoulders where higher stress was found.
Date: May 1, 2009
Creator: Lam, P; Philip Zapp, P; Jonathan Duffey, J & Kerry Dunn, K
Partner: UNT Libraries Government Documents Department

Integrated thermal-microstructure model to predict the property gradients in resistance spot steel welds

Description: An integrated model approach was proposed for relating resistance welding parameters to weldment properties. An existing microstructure model was used to determine the microstructural and property gradients in resistance spot welds of plain carbon steel. The effect of these gradients on the weld integrity was evaluated with finite element analysis. Further modifications to this integrated thermal-microstructure model are discussed.
Date: November 1, 1998
Creator: Babu, S.S.; Riemer, B.W.; Santella, M.L. & Feng, Z.
Partner: UNT Libraries Government Documents Department

Modeling of residual stresses by HY-100 weldments

Description: Residual stress distribution in a HY-100 steel disk, induced by GTA spot welding, was analyzed by finite element (FE) formulations and measured by neutron diffraction (ND). Computations used temperature- dependent thermophysical and mechanical properties. FE model predictions are in good agreement with ND data in far heat affected zone (HAZ) and in base metal. Predicted residual stresses in fusion zone and near HAZ were higher than those measured by ND. This discrepancy was attributed to microstructural changes and associated material properties in the HAZ and fusion zone due to phase transformations during the weld thermal cycle.
Date: February 1, 1997
Creator: Zacharia, T.; Taljat, B. & Radhakrishnan, B.
Partner: UNT Libraries Government Documents Department

Neutron diffraction studies of welds of aerospace aluminum alloys

Description: Neutron diffraction and electron microscopy were done on residual stress in various regions comprising variable polarity plasma arc welds of alloys 2219 (Al-6.3Cu) and 2195 (Al-4.0Cu-1.0Li-0.5Mg-0.5Ag). Results indicate that lattice parameter changes in the various weld regions may be attributed to residual stresses generated during welding, as well as local changes in microstructure. Distribution of longitudinal and transverse stress of welded panels shows peaks of tension and compression, respectively, within the HAZ and corroborate earlier theoretical results. Position of these peaks are related to position of minimum strength within the HAZ, and the magnitude of these peaks are a fraction of the local yield strength in this region. Weldments of alloy 2195-T8 exhibited higher peak residual stress than alloy 2219-T87. Comparison of neutron diffraction and microstructural analysis indicate decreased lattice parameters associated with the solid solution of the near HAZ; this results in decreased apparent tensile residual stress within this region and may significantly alter interpretation of residual stress measurements of these alloys. Considerable relaxation of residual stress occurs during removal of specimens from welded panels and was used to aid in differentiating changes in lattice parameters attributed to residual stress from welding and modifications in microstructure.
Date: October 1, 1996
Creator: Martukanitz, R.P.; Howell, P.R.; Payzant, E.A.; Spooner, S. & Hubbard, C.R.
Partner: UNT Libraries Government Documents Department

Optical and analytical electron microscopy of ductility-dip cracking in Ni-base filler metal 52 -- Initial studies

Description: Microcharacterization studies were performed on weld-metal microstructures of a Ni-base filler metal. Specimens were taken from the fusion zone and the weld-metal heat-affected zone of transverse- and spot-Varestraint welds. The filler metal was first deposited onto a steel substrate by hot-wire, gas tungsten arc welding before specimen removal. Optical microscopy indicates the crack morphology is intergranular and is along high-angle, migrated grain boundaries. At low magnifications, scanning electron microscopy reveals a relatively smooth fracture surface. However, at higher magnifications the grain faces exhibit microductility. Analytical electron microscopy reveals high-angle, migrated grain boundaries decorated with MC (Ti, Cr) and M{sub 23}C{sub 6} (Cr, Ni, Fe) precipitates ranging from 10 to 200 n. Auger electron spectroscopy of pre-strained Gleeble specimens fractured in situ revealed internal ductility-dip cracks decorated with magnesium aluminate (MgAl{sub 2}O{sub 4}) spinel particles (1,000 nm).
Date: January 1, 1998
Creator: Cola, M.J. & Teter, D.F.
Partner: UNT Libraries Government Documents Department

Role of beam absorption in plasma during laser welding

Description: The relationship between beam focus position and penetration depth in CW laser welding was studied numerically and experimentally for different welding conditions. Calculations were performed using a transient hydrodynamic model that incorporates the effect of evaporation recoil pressure and the associated melt expulsion. The simulation results are compared with measurements made on a series of test welds obtained using a 1650 W CO{sub 2} laser. The simulations predict, and the experiments confirm, that maximum penetration occurs with a specific location of the beam focus, with respect to the original sample surface, and that this relationship depends on the processing conditions. In particular, beam absorption in the plasma has a significant effect on the relationship between penetration and focus position. When the process parameters result in strong beam absorption in the keyhole plasma, the maximum penetration will occur when the laser focus is at or above the sample surface. In a case of weak absorption however, the penetration depth reaches its maximum value when the beam focus is located below the sample surface. In all cases, the numerical results are in good agreement with the experimental measurements.
Date: May 15, 2000
Creator: SEMAK,V.V.; STEELE,R.J.; FUERSCHBACH,PHILLIP W. & DAMKROGER,BRIAN K.
Partner: UNT Libraries Government Documents Department

Aging and phase stability of waste package outer barrier

Description: After aging for 16,000 hr at 593 C, P phase was found at Alloy 22 grain boundaries. At higher temperatures (as much as 760 C for the same aging time), both {mu} and P phase formed on grain boundaries and within the grains. Grain boundary carbides also form at 593 C and higher, but the amount of carbide is small compared to the p and P phases. A small amount of sigma phase forms in Alloy 22 after 16,000 hr at 704 and 760 C. LRO was seen after aging for 16,000 hr at 593 C and for 40,000 hr at 427 C, but ordering most likely begins at shorter times. More work must be done in phase identification. Samples aged at times less than 16,000 hr must be examined so that the phase evolution during aging can be determined. A procedure being developed for phase extraction and x-ray diffraction should make phase identification and quantification of the relative amounts of each phase easier. The times at which various stages of intermetallic precipitation occur in Alloy 22 base metal displayed an exponential (Arrhenius-type) temperature dependence. The activation energy was determined to be 290 kJ/mol. A more quantitative model based on precipitate volume fraction measurements that can be integrated over a variable temperature profile must be developed before a reasonable prediction of the phase stability of Alloy 22 base metal under repository conditions can be made. In addition, the effect of intermetallic and carbide precipitation on Alloy 22 properties must be determined. Precipitation kinetics in weld heat-affected zones, as well as in the base metal, must be studied because the thermal pulse given the HAZ during the welding process may alter nucleation of intermetallics and therefore the precipitation kinetics. Intermetallic and carbide precipitates form in Alloy 22 welds during the welding ...
Date: July 14, 1999
Creator: Summers, T & Turchi, P
Partner: UNT Libraries Government Documents Department

Stress corrosion cracking of austenitic stainless steel core internal welds.

Description: Microstructural analyses by several advanced metallographic techniques were conducted on austenitic stainless steel mockup and core shroud welds that had cracked in boiling water reactors. Contrary to previous beliefs, heat-affected zones of the cracked Type 304L, as well as 304 SS core shroud welds and mockup shielded-metal-arc welds, were free of grain-boundary carbides, which shows that core shroud failure cannot be explained by classical intergranular stress corrosion cracking. Neither martensite nor delta-ferrite films were present on the grain boundaries. However, as a result of exposure to welding fumes, the heat-affected zones of the core shroud welds were significantly contaminated by oxygen and fluorine, which migrate to grain boundaries. Significant oxygen contamination seems to promote fluorine contamination and suppress thermal sensitization. Results of slow-strain-rate tensile tests also indicate that fluorine exacerbates the susceptibility of irradiated steels to intergranular stress corrosion cracking. These observations, combined with previous reports on the strong influence of weld flux, indicate that oxygen and fluorine contamination and fluorine-catalyzed stress corrosion play a major role in cracking of core shroud welds.
Date: April 14, 1999
Creator: Chung, H. M.; Park, J.-H.; Ruther, W. E.; Sanecki, J. E.; Strain, R. V. & Zaluzec, N. J.
Partner: UNT Libraries Government Documents Department

The Stress-Relief Cracking Susceptibility of a New Ferritic Steel - Part I: Single-Pass Heat-Affected Zone Simulations

Description: The stress-relief cracking susceptibility of single-pass welds in a new ferritic steel, HCM2S, has been evaluated and compared to 2.25Cr-1Mo steel using Gleeble techniques. Simulated coarse-grained heat-affected zones (CGHAZ) were produced under a range of energy inputs and tested at various post-weld heat treatment (PWHT) temperatures. Both alloys were tested at a stress of 325 MPa. The 2.25 Cr-1Mo steel was also tested at 270 MPa to normalize for the difference in yield strength between the two materials. Light optical and scanning electron microscopy were used to characterize the CGHAZ microstructure. The ''as-welded'' CGHAZ of each alloy consisted of lath martensite or bainite and had approximately equal prior austenite grain sizes. The as-welded hardness of the 2.25Cr-1Mo steel CGHAZ was significantly higher than that of the HCM2S alloy. Over the range studied energy input had no effect on the as-welded microstructure or hardness of either alloy. The energy input also had no effect on the stress-relief cracking susceptibility of either material. Both alloys failed intergranularly along prior austenite grain boundaries under all test conditions. The 2.25Cr-1Mo steel samples experienced significant macroductility and some microductility when tested at 325 MPa. The ductility decreased significantly when tested at 270 MPa but was still higher that than of HCM2S at each test condition. The time to failure decreased with increasing PWHT Temperature for each material. There was no significant difference in the times to failure between the two materials. Varying energy input and stress had no effect on the time-to failure. The ductility, as measured by reduction in are% increased with increasing PWHT temperature for 2.25 Cr-1Mo steel tested at both stresses. However, PWHT temperature had no effect on the ductility of HCM2S. The hardness of the CGHAZ for 2.25Cr-1Mo steel decreased significantly after PWHT, but remained constant for HCM2S. The differences in ...
Date: December 15, 1999
Creator: NAWROCKI,J.G.; DUPONT,J.N.; ROBINO,CHARLES V. & MARDER,A.R.
Partner: UNT Libraries Government Documents Department

Towards a reliable laser spray powder deposition system through process characterization

Description: A series of experiments have been performed to characterize the laser spray powder deposition tea-one (HAZ) in the process. Goal of these experiments was to minimize the heat affected base substrate while obtaining a maximum build-up rate of the deposited material. Response surface models have been developed to achieve this goal. These models indicate that laser irradiance and component travel speed are both important factors to be considered in optimization of this process. These models suggest that a minimum HAZ can be obtained with a maximum material build-up height by maintaining with a slow travel speed. Although these models are useful in identifying significant factor and process trends, further refinement is required for practical use in industrial applications. Weighting of the response variables used in generating the models is being considered to improve the model robustness. High speed imaging of the deposition process suggests that the powder particle size and/or size distribution affects the stability of this process.
Date: July 1, 1995
Creator: Keicher, D.M.; Jellison, J.L.; Schanwald, L.P.; Romero, J.A. & Abbott, D.H.
Partner: UNT Libraries Government Documents Department

Direct Observation of Phase Transformations in Austenitic Stainless Steel Welds Using In-situ Spatially Resolved and Time-resolved X-ray Diffraction

Description: Spatially resolved x-ray diffraction (SRXRD) and time resolved x-ray diffraction (TRXRD) were used to investigate real time solid state phase transformations and solidification in AISI type 304 stainless steel gas tungsten arc (GTA) welds. These experiments were conducted at Stanford Synchrotron Radiation Laboratory (SSRL) using a high flux beam line. Spatially resolved observations of {gamma} {leftrightarrow} {delta} solid state phase transformations were performed in the heat affected zone (HAZ) of moving welds and time-resolved observations of the solidification sequence were performed in the fusion zone (FZ) of stationary welds after the arc had been terminated. Results of the moving weld experiments showed that the kinetics of the {gamma}{yields}{delta} phase transformation on heating in the HAZ were sufficiently rapid to transform a narrow region surrounding the liquid weld pool to the {delta} ferrite phase. Results of the stationary weld experiments showed, for the first time, that solidification can occur directly to the {delta} ferrite phase, which persisted as a single phase for 0.5s. Upon solidification to {delta}, the {delta} {yields} {gamma} phase transformation followed and completed in 0.2s as the weld cooled further to room temperature.
Date: September 23, 1999
Creator: Elmer, J.; Wong, J. & Ressler, T.
Partner: UNT Libraries Government Documents Department

INVESTIGATION IN HARDSURFACING A NICKEL-COPPER ALLOY (MONEL400).

Description: Brookhaven National Laboratory (BNL) investigated the causes of weldability problems and materials failures encountered with the application of Monel (Ni-Cu) 400 as a base material and Stellite 6 (Co-Cr) as the hard-surfacing material when using the oxyacetylene welding process. This work was performed under a cooperative research and development agreement (CRADA) with the Target Rock Division of the Curtiss-Wright Flow Control Corporation. BNL evaluated two heats of Monel 400 material. One of the heats had performed well during manufacturing, producing an acceptable number of ''good'' parts. The second heat had produced some good parts but also exhibited a peculiar type of hardsurfacing/base metal collapse during the welding process. A review of the chemistry on the two heats of material indicated that they both met the chemical requirements for Monel400. During examination of the failed component, linear indications (cracks) were evident on the valve body, both on the circumferential area (top of valve body) and below the hard surfaced weld deposit. independent measurements also indicated that the two heats met the specification requirement for the material. The heat affected zone (HAZ) also contained linear discontinuities. The valve body was welded using the oxyacetylene welding process, a qualified and skilled welder, and had been given a pre-heat of between 1400-1600 F (760-871 C), which is the Target Rock qualified procedure requirement. Both original suppliers performed mechanical testing on their material that indicated the two heats also met the mechanical property requirements of the specification. The BNL investigation into the cause of the differences between these heats of material utilized the following techniques: (1) Heat Treatment of both heats of material; (2) Hardness testing; (3) Optical microscopy; (4) Scanning electron microscope (SEM)/Fractography; and (5) Energy dispersive spectroscopy (EDS). The report concludes that the cause of the failure of the valve body during welding ...
Date: December 1, 2001
Creator: CZAJKOWSKI,C. & BUTTERS,M.
Partner: UNT Libraries Government Documents Department

Observations of Ferrite/Austenite Transformations in the Heat Affected Zone of 2205 Duplex Stainless Steel Spot Welds Using Time Resolved X-Ray Diffraction

Description: Time Resolved X-Ray Diffraction (TRXRD) measurements are made in the Heat Affected Zone (HAZ) of 2205 Duplex Stainless Steel (DSS) spot welds. Both the {gamma} {yields} {delta} and {delta} {yields} {gamma} transformations are monitored as a function of time during the rapid spot weld heating and cooling cycles. These observations are then correlated with calculated thermal cycles. Where the peak temperatures are highest ({approx}1342 C), the {gamma} {yields} {delta} transformation proceeds to completion, leaving a ferritic microstructure at the end of heating. With lower peak temperatures, the {gamma} {yields} {delta} transformation proceeds to only partial completion, resulting in a microstructure containing both transformed and untransformed austenite. Further analyses of the individual diffraction patterns show shifts in the peak positions and peak widths as a function of both time and temperature. In addition, these changes in the peak characteristics are correlated with measured changes in the ferrite volume fraction. Such changes in the peak positions and widths during the {gamma} {yields} {delta} transformation provide an indication of changes occurring in each phase. These changes in peak properties can be correlated with the diffusion of nitrogen and other substitutional alloying elements, which are recognized as the primary mechanisms for this transformation. Upon cooling, the {delta} {yields} {gamma} transformation is observed to proceed from both the completely and partially transformed microstructural regions in the TRXRD data. An examination of the resulting microstructures confirms the TRXRD observation as the evidence shows that austenite both nucleates and grows from the ferritic microstructure at locations closest to the fusion zone boundary and grows from untransformed austenite grains at locations further from this boundary.
Date: October 29, 2003
Creator: Palmer, T; Elmer, J & Babu, S
Partner: UNT Libraries Government Documents Department

DETERMINATION OF CORROSION INHIBITOR CRITERIA FOR TYPE III/IIIA TANKS DURING SALT DISSOLUTION OPERATIONS INTERIM REPORT

Description: Preparation of high level waste for vitrification involves in part the dissolution of salt cake from the carbon steel storage tanks. During dissolution, a point is reached in which the corrosion inhibitors, hydroxide and nitrite, are diluted below established guidelines, and nitrate stress corrosion cracking (SCC) is possible. Because the addition of inhibitors may be counterproductive to process efficiency and waste minimization, corrosion testing was initiated to revisit and possibly revise the guidelines for inhibitor limits. The bases for the work summarized in this status report are results from previously-completed phases of study. In the first two phases of study, several reduced-inhibitor levels were tested in HLW simulants with nitrate concentrations ranging from 4.5 M to 8.5 M. The first two phases of work determined, among other things, the reduced-inhibitor levels and solution chemistries in which heat-treated and non-heat-treated A537 carbon steel is susceptible to SCC, crevice corrosion, and pitting. The work covered in this current task both builds on and verifies the conclusions of the previous work. The current work involves testing of low levels of inhibitors in HLW simulants with 5.5 M to 8.5 M nitrate concentrations. Stressed U-bend specimens, both polarized and non-polarized, were tested. Non-polarized U-bend testing is ongoing, with the U-bends currently in test for 100 days. The purpose of the testing is to determine SCC susceptibility in the vapor space (VS) and liquid air interface (LAI) regions of the HLW tanks under conditions expected during salt dissolution, and also to verify previous accelerated testing. The simulated wastes being tested have nitrate concentrations of 5.5 M and 8.5 M and inhibitor levels of 0.01 M/0.01 M hydroxide/nitrite and 0.1 M/ 0.1 M hydroxide/nitrite. The open circuit potential measurements being monitored and the corrosion morphology of the U-bends are in agreement with results and observations of ...
Date: December 31, 2007
Creator: Counts, K; Bruce Wiersma, B & John Mickalonis, J
Partner: UNT Libraries Government Documents Department

Direct Observations of the (Alpha to Gamma) Transformation at Different Input Powers in the Heat Affected Zone of 1045 C-Mn Steel Arc Welds Observed by Spatially Resolved X-Ray Diffraction

Description: Spatially Resolved X-Ray Diffraction (SRXRD) experiments have been performed during Gas Tungsten Arc (GTA) welding of AISI 1045 C-Mn steel at input powers ranging from 1000 W to 3750 W. In situ diffraction patterns taken at discreet locations across the width of the heat affected zone (HAZ) near the peak of the heating cycle in each weld show regions containing austenite ({gamma}), ferrite and austenite ({alpha}+{gamma}), and ferrite ({alpha}). Changes in input power have a demonstrated effect on the resulting sizes of these regions. The largest effect is on the {gamma} phase region, which nearly triples in width with increasing input power, while the width of the surrounding two phase {alpha}+{gamma} region remains relatively constant. An analysis of the diffraction patterns obtained across this range of locations allows the formation of austenite from the base metal microstructure to be monitored. After the completion of the {alpha} {yields} {gamma} transformation, a splitting of the austenite peaks is observed at temperatures between approximately 860 C and 1290 C. This splitting in the austenite peaks results from the dissolution of cementite laths originally present in the base metal pearlite, which remain after the completion of the {alpha} {yields} {gamma} transformation, and represents the formation of a second more highly alloyed austenite constituent. With increasing temperatures, carbon, originally present in the cementite laths, diffuses from the second newly formed austenite constituent to the original austenite constituent. Eventually, a homogeneous austenitic microstructure is produced at temperatures of approximately 1300 C and above, depending on the weld input power.
Date: March 16, 2005
Creator: Palmer, T A & Elmer, J W
Partner: UNT Libraries Government Documents Department

PREDICTION OF DISSOLVER LIFETIMES THROUGH NON-DESTRUCTIVE EVALUATION AND LABORATORY TESTING

Description: Non-destructive evaluation was used as the primary method of monitoring the corrosion degradation of nuclear material dissolvers and assessing the remaining lifetimes. Materials were typically processed in nitric acid based (4-14M) solutions containing fluoride concentrations less than 0.2 M. The primary corrosion issue for the stainless steel dissolvers is the occurrence of localized corrosion near the tank bottom and the heat affected zones of the welds. Laboratory data for a range of operational conditions, including solution chemistry and temperature, was used to assess the impact of processing changes on the dissolver corrosion rate. Experimental and NDE-based general corrosion rates were found to be in reasonable agreement for standard dissolution chemistries consisting of nitric acid with fluorides and at temperatures less than 95 C. Greater differences were observed when chloride was present as an impurity and temperatures exceeded 100 C.
Date: October 3, 2011
Creator: Mickalonis, J.; Woodsmall, T.; Hinz, W. & Edwards, T.
Partner: UNT Libraries Government Documents Department

Laser welding and post weld treatment of modified 9Cr-1MoVNb steel.

Description: Laser welding and post weld laser treatment of modified 9Cr-1MoVNb steels (Grade P91) were performed in this preliminary study to investigate the feasibility of using laser welding process as a potential alternative to arc welding methods for solving the Type IV cracking problem in P91 steel welds. The mechanical and metallurgical testing of the pulsed Nd:YAG laser-welded samples shows the following conclusions: (1) both bead-on-plate and circumferential butt welds made by a pulsed Nd:YAG laser show good welds that are free of microcracks and porosity. The narrow heat affected zone has a homogeneous grain structure without conventional soft hardness zone where the Type IV cracking occurs in conventional arc welds. (2) The laser weld tests also show that the same laser welder has the potential to be used as a multi-function tool for weld surface remelting, glazing or post weld tempering to reduce the weld surface defects and to increase the cracking resistance and toughness of the welds. (3) The Vicker hardness of laser welds in the weld and heat affected zone was 420-500 HV with peak hardness in the HAZ compared to 240 HV of base metal. Post weld laser treatment was able to slightly reduce the peak hardness and smooth the hardness profile, but failed to bring the hardness down to below 300 HV due to insufficient time at temperature and too fast cooling rate after the time. Though optimal hardness of weld made by laser is to be determined for best weld strength, methods to achieve the post weld laser treatment temperature, time at the temperature and slow cooling rate need to be developed. (4) Mechanical testing of the laser weld and post weld laser treated samples need to be performed to evaluate the effects of laser post treatments such as surface remelting, glazing, re-hardening, or tempering ...
Date: April 3, 2012
Creator: Xu, Z. (Nuclear Engineering Division)
Partner: UNT Libraries Government Documents Department

Weldability Comparison of Tritium-Charged-and -Aged 304 and 316LN Stainless Steels

Description: Measurement of the effects of helium (from tritium decay) on the weldability of Types 304 and ITER Grade 316LN stainless steel demonstrated the inherent complexities in designing and conducting an experimental program using tritium-charged-and-aged materials to simulate the effects of irradiation-induced helium on weld behavior. Differences in microstructure, surface condition and alloy chemistry are known to play key roles in tritium absorption and distribution and thus have direct effects on the subsequent 3He production and distribution. The helium embrittlement cracking produced in 0.5 in. (12.7 mm) thick 304 and 316LN plates that were tritium-charged in the same container and subsequently welded with gas metal arc, low heat input weld overlays and gas tungsten arc stringer beads, varied markedly. For example, the porosity in the weld beads was much higher in the 304 plate than in the 316LN plate. Additionally, crack measurements from weld cross-sections revealed more extensive intergranular cracking in the heat-affected zones of welds on the 304 plate when compared to the 316LN plate. However, the differences between the two types of stainless steel may not be a result of differences in the resistance to helium embrittlement cracking, but may be due to initial tritium concentration differences developed in the as-charged plates. Further work is necessary to identify the reasons for the apparent plate to plate variation in tritium/helium content and to demonstrate the similarities (or differences) between Types 304 and ITER grade 316LN stainless steel.
Date: June 10, 2003
Creator: Tosten, M.H.
Partner: UNT Libraries Government Documents Department

Modeling the ferrite-to-austenite transformation in the heat-affected zone of stainless steel multi-pass welds

Description: The ferrite/austenite transformation in austenitic stainless steel welds was modeled by considering the transformation as a diffusion-controlled process. A finite-difference method was used to solve the diffusion equations. The transformation behavior was evaluated for both isothermal aging and linear cooling over a range of cooling rates. The analysis provides information on the change in ferrite content as a function of heat treatment as well as the rate of the formation (or dissolution) of ferrite. The compositions of the ferrite and austenite are also obtained in the analysis. the results show that the approach to equilibrium can often be indirect and sometimes counter to intuition. The analysis is useful in providing information on the microstructural stability in austenitic stainless steel welds that cannot be obtained experimentally.
Date: December 31, 1995
Creator: Vitek, J.M.; Vitek, S.A. & David, S.A.
Partner: UNT Libraries Government Documents Department