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Real-time monitoring of laser surface hardening of ferrous alloys.

Description: An infrared process monitor was used to monitor in real-time the infrared emissions during laser surface hardening of gray cast iron and 1045 steel. The signal from the monitor was correlated with the hardness and case depth of the laser-treated tracks. Test data show that a linear relationship exists between the monitor output DC level voltage and hardness up to the maximum hardness possible and also between the monitor output DC level voltage and case depth. This simple relationship of the monitor voltage signal with hardness and case depth makes it easy to monitor process hardness, case depth and quality. A calibration test on prototypic material can be used to determine at what voltage level melting occurs and the heat treating process hardness and case depth can be monitored easily by setting an upper and lower bound for the voltage signal. The monitor is also capable of tracking changes in surface quality or flatness of the part that is being treated.
Date: September 30, 1999
Creator: Xu, Z.; Leong, K. H. & Reed, C. B.
Partner: UNT Libraries Government Documents Department

Excimer laser processing of tool steel: Tribological effects of multiple pulse processing and titanium alloying

Description: Excimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V, high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy. Hardness and modulus were not significantly affected by the treatment, but friction in dry sliding against an alumina pin was reduced. The reduction was small but persistent for multiply melted and resolidified surfaces. These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately 1000 cycles, indicating wear=through of the modified surface. The observed properties will be discussed in terms of the excimer laser modification process and the microstructure and composition of the resulting surfaces.
Date: December 1, 1995
Creator: Jervis, T.R.; Nastasi, M.; Griffin, A.J. Jr.; Zocco, T.G.; Taylor, T.N. & Foltyn, S.R.
Partner: UNT Libraries Government Documents Department

Surface Hardening by Nanoparticle Precipitation in Ni(Al,O)

Description: Ion implantation of O and Al were used to form nanometer-size precipitates of NiO or Al{sub 2}O{sub 3} in the near-surface of Ni. The yield strengths of the treated layers were determined by nanoindentation testing in conjunction with finite-element modeling. The strengths range up to {approximately}5 GPa, substantially above values for hard bearing steels. These results agree quantitatively with predictions of dispersion-hardening theory based on the precipitate microstructures observed by transmission electron microscopy. Such surface hardening by ion implantation may be beneficial for Ni components in micro-electromechanical systems.
Date: April 1, 2001
Partner: UNT Libraries Government Documents Department

Pulsed laser surface hardening of ferrous alloys.

Description: A high power pulsed Nd:YAG laser and special optics were used to produce surface hardening on 1045 steel and gray cast iron by varying the process parameters. Unlike CO{sub 2} lasers, where absorptive coatings are required, the higher absorptivity of ferrous alloys at the Nd:YAG laser wavelength eliminates the necessity of applying a coating before processing. Metallurgical analysis of the treated tracks showed that very fine and hard martensitic microstructure (1045 steel) or inhomogeneous martensite (gray cast iron) were obtained without surface melting, giving maximum hardness of HRC 61 and HRC 40 for 1045 steel and gray cast iron respectively. The corresponding maximum case depths for both alloys at the above hardness are 0.6 mm. Gray cast iron was more difficult to harden without surface melting because of its lower melting temperature and a significantly longer time-at-temperature required to diffuse carbon atoms from the graphite flakes into the austenite matrix during laser heating. The thermal distortion was characterized in term of flatness changes after surface hardening.
Date: September 30, 1999
Creator: Xu, Z.; Reed, C. B.; Leong, K. H. & Hunter, B. V.
Partner: UNT Libraries Government Documents Department

Modeling of Ion Beam Surface Treatment

Description: Use of intense pulsed ion beams is providing a new capability for surface engineering based on rapid thermal processing of the top few microns of metal, ceramic, and glass surfaces. The Ion Beam Surface Treatment (IBEST) process is shown to produce enhancements in the hardness, corrosion, wear, and fatigue properties of surfaces by rapid melt and resolidification. We have created a new coe IBMOD that enables modeling of intense ion beam deposition and the resulting rapid thermal cycling of surfaces. This code has been used to model the effect of treatment of Al, Fe, and Ti using different ion species and pulse durations.
Date: June 1, 1996
Creator: Stinnett, R.W.; Maenchen, J.E.; Renk, T.J.; Struve, K.W. & Campbell, M.M.
Partner: UNT Libraries Government Documents Department

Examination of Compatibility of Potentially Cavitation-Resistant Modifications of Type 316LN Stainless Steel with Mercury in a Thermal Convection Loop

Description: A 316L stainless steel thermal convection loop (TCL) containing a variety of stainless steel coupons circulated mercury for 2000 h. The TCL conditions included a maximum temperature of 307 C, a maximum temperature gradient of 90 C, and a Hg velocity of about 1.4 m/min. In addition to mill-annealed/surface-ground 316LN coupons serving as the baseline material, other coupons included 316LN that was 50% cold-worked, 316LN that was given a proprietary surface hardening treatment termed ''kolsterizing,'' and Nitronic 60. The purpose of this test was to examine Hg compatibility with these modest variations of annealed 31 6LN stainless steel that are considered potential improvements over annealed 31 6LN for cavitation-erosion resistance in the Spallation Neutron Source (SNS) target containment system. The results indicated negligible weight change for each coupon type, no significant indication of attack or surface roughening, and generally no interaction with Hg.
Date: August 29, 2002
Creator: Pawel, SJ
Partner: UNT Libraries Government Documents Department

Hard-facing with electro-spark deposition. Final report

Description: A common method to improve wear resistance of metals in rubbing contact is to increase their surface hardness. Electro-Spark Deposition is a process which uses capacitive discharge pulses of high current passing through a hard carbide electrode in contact with and scanning the metal surface to be hardened. The result is a thin, hard, adherent coating of carbide deposited with a minimum of heat influence on the substrate and a significant increase in wear life of the coated metal. Electro-Spark Deposition is similar to a micro-welding process. It is a simple, portable and inexpensive coating method, which has great potential for commercial utilization. This thesis is an in depth study of the parameters associated with the ESD process and the wear resistance of the coatings.
Date: January 1, 1983
Creator: Kees, K.P.
Partner: UNT Libraries Government Documents Department

Friction Stir Processing for Efficient Manufacturing

Description: Friction at contacting surfaces in relative motion is a major source of parasitic energy loss in machine systems and manufacturing processes. Consequently, friction reduction usually translates to efficiency gain and reduction in energy consumption. Furthermore, friction at surfaces eventually leads to wear and failure of the components thereby compromising reliability and durability. In order to reduce friction and wear in tribological components, material surfaces are often hardened by a variety of methods, including conventional heat treatment, laser surface hardening, and thin-film coatings. While these surface treatments are effective when used in conjunction with lubrication to prevent failure, they are all energy intensive and could potentially add significant cost. A new concept for surface hardening of metallic materials and components is Friction Stir Processing (FSP). Compared to the current surface hardening technologies, FSP is more energy efficient has no emission or waste by products and may result in better tribological performance. FSP involves plunging a rotating tool to a predetermined depth (case layer thickness) and translating the FSP tool along the area to be processed. This action of the tool produces heating and severe plastic deformation of the processed area. For steel the temperature is high enough to cause phase transformation, ultimately forming hard martensitic phase. Indeed, FSP has been used for surface modification of several metals and alloys so as to homogenize the microstructure and refine the grain size, both of which led to improved fatigue and corrosion resistance. Based on the effect of FSP on near-surface layer material, it was expected to have beneficial effects on friction and wear performance of metallic materials. However, little or no knowledge existed on the impact of FSP concerning friction and wear performance the subject of the this project and final report. Specifically for steel, which is the most dominant tribological material, FSP ...
Date: January 31, 2012
Creator: Smith, Mr. Christopher B. & Ajayi, Dr. Oyelayo
Partner: UNT Libraries Government Documents Department

Low Temperature Surface Carburization of Stainless Steels

Description: Low-temperature colossal supersaturation (LTCSS) is a novel surface hardening method for carburization of austenitic stainless steels (SS) without the precipitation of carbides. The formation of carbides is kinetically suppressed, enabling extremely high or colossal carbon supersaturation. As a result, surface carbon concentrations in excess of 12 at. % are routinely achieved. This treatment increases the surface hardness by a factor of four to five, improving resistance to wear, corrosion, and fatigue, with significant retained ductility. LTCSS is a diffusional surface hardening process that provides a uniform and conformal hardened gradient surface with no risk of delamination or peeling. The treatment retains the austenitic phase and is completely non-magnetic. In addition, because parts are treated at low temperature, they do not distort or change dimensions. During this treatment, carbon diffusion proceeds into the metal at temperatures that constrain substitutional diffusion or mobility between the metal alloy elements. Though immobilized and unable to assemble to form carbides, chromium and similar alloying elements nonetheless draw enormous amounts of carbon into their interstitial spaces. The carbon in the interstitial spaces of the alloy crystals makes the surface harder than ever achieved before by more conventional heat treating or diffusion process. The carbon solid solution manifests a Vickers hardness often exceeding 1000 HV (equivalent to 70 HRC). This project objective was to extend the LTCSS treatment to other austenitic alloys, and to quantify improvements in fatigue, corrosion, and wear resistance. Highlights from the research include the following: • Extension of the applicability of the LTCSS process to a broad range of austenitic and duplex grades of steels • Demonstration of LTCSS ability for a variety of different component shapes and sizes • Detailed microstructural characterization of LTCSS-treated samples of 316L and other alloys • Thermodynamic modeling to explain the high degree of carbon solubility possible ...
Date: December 7, 2007
Creator: Collins, Sunniva R.; Heuer, Arthur H. & Sikka, Vinod K.
Partner: UNT Libraries Government Documents Department

Inside Sandia

Description: Articles in this issue include ``Molten salt corrosion testing,`` ``Pulsed ion beams for thermal surface treatment: Improved corrosion, wear, and hardness properties at low cost,`` ``Unmasking hidden armaments: Superconducting gravity sensor could find underground weapons, bunkers,`` ``Charbroiled burgers, heterocyclic amines, and cancer: Molecular modeling identifies dangerous mutagens,`` ``Revolutionary airbag offers increased safety options,`` ``EcoSys{sup TM}: an expert system for `Green Design` ``, ``Sandia, salt, and oil: Labs` diagnostics and analysis help maintain vital US oil reserve,`` and ``Automated fixture design speeds development for prototypes and production``.
Date: December 31, 1995
Partner: UNT Libraries Government Documents Department

Cluster carburizing. Progress report, June 1, 1977--May 31, 1978

Description: When aging quenched Ta-27% Hf alloys at 685/sup 0/C, excess thermal vacancies were found to condense into vacancy loops. The loops are responsible for the first age-hardening peak observed during heat treatment. In a study of binary alloys formed by two monocarbides, a miscibility gap was found in the NbC-HfC system with a critical temperature between 1100--1200/sup 0/C, while homogeneous solutions were formed by TaC-HfC down to 1000/sup 0/C. An investigation of solid phase carburizing of Ta-Hf and Nb-Hf alloys indicated that this technique results in a higher carbon activity, but slower kinetics than was obtained by gas carburizing. Work continues on improving this technique and on preparing cluster carburized specimens for study by transmission electron microscopy.
Date: February 1, 1978
Creator: Morral, J.E.
Partner: UNT Libraries Government Documents Department

Cluster carburizing. Final report, June 1, 1973-May 31, 1979

Description: Three major accomplishments of the cluster carburizing program were showing that the hardness of aged and carburized materials could be controlled via the aged structure; developing a new and analytical theory of subscale formation; and characterizing the properties of Ta-Hf alloys with respect to precipitation kinetics and morphology, diffusion kinetics, age hardening, and subscale formation. The first of these verified the cluster carburizing concept, which has potential use in the development of high strength materials. The second has applications in the fields of hot corrosion, oxidation, and high temperature coatings. The third provided necessary background for this study and provided a further understanding of the behavior of refractory metals. Details about the above are contained in this final report as well as comments on the Ta-Hf, TaC-HfC and NbC-HfC phase diagrams, a comparison of hardening in the Nb-Hf and Ta-Hf system, and a discussion of possible future work.
Date: May 1, 1979
Creator: Morral, J.E.
Partner: UNT Libraries Government Documents Department

Carburization of austenitic alloys by gaseous impurities in helium

Description: The carburization behavior of Alloy 800H, Inconel Alloy 617 and Hastelloy Alloy X in helium containing various amounts of H/sub 2/, CO, CH/sub 4/, H/sub 2/O and CO/sub 2/ was studied. Corrosion tests were conducted in a temperature range from 649 to 1000/sup 0/C (1200 to 1832/sup 0/F) for exposure time up to 10,000 h. Four different helium environments, identified as A, B, C, and D, were investigated. Concentrations of gaseous impurities were 1500 ..mu..atm H/sub 2/, 450 ..mu..atm CO, 50 ..mu..atm CH/sub 4/ and 50 ..mu..atm H/sub 2/O for Environment A; 200 ..mu..atm H/sub 2/, 100 ..mu..atm CO, 20 ..mu..atm CH/sub 4/, 50 ..mu..atm H/sub 2/O and 5 ..mu..atm CO/sub 2/ for Environment B; 500 ..mu..atm H/sub 2/, 50 ..mu..atm CO, 50 ..mu..atm CH/sub 4/ and < 0.5 ..mu..atm H/sub 2/O for Environment C; and 500 ..mu..atm H/sub 2/, 50 ..mu..atm CO, 50 ..mu..atm CH/sub 4/ and 1.5 ..mu..atm H/sub 2/O for Environment D. Environments A and B were characteristic of high-oxygen potential, while C and D were characteristic of low-oxygen potential. The results showed that the carburization kinetics in low-oxygen potential environments (C and D) were significantly higher, approximately an order of magnitude higher at high temperatures, than those in high-oxygen potential environments (A and B) for all three alloys. Thermodynamic analyses indicated no significant differences in the thermodynamic carburization potential between low- and high-oxygen potential environments. It is thus believed that the enhanced carburization kinetics observed in the low-oxygen potential environments were related to kinetic effects. A qualitatively mechanistic model was proposed to explain the enhanced kinetics. The present results further suggest that controlling the oxygen potential of the service environment can be an effective means of reducing carburization of alloys.
Date: March 1, 1980
Creator: Lai, G.Y. & Johnson, W.R.
Partner: UNT Libraries Government Documents Department

Effect of sodium environment on the creep-rupture and low-cycle fatigue behavior of austenitic stainless steels

Description: Austenitic stainless steels used for in-core structural components, piping, valves, and the intermediate heat exchanger in Liquid-Metal Fast-Breeder Reactors (LMFBRs) are subjected to sodium at elevated temperatures and to complex stress conditions. As a result, the materials can undergo compositional and microstructural changes as well as mechanical deformation by creep and cyclic fatigue processes. Information is presented on the creep-rupture and low-cycle fatigue behavior of Types 304 and 316 stainless steel in the solution-annealed condition and after long-term exposure to flowing sodium. The nonmetallic impurity-element concentrations in the sodium were controlled at levels similar to those in EBR-II primary sodium. Strain-time relationships developed from the experimental creep data were used to generate isochronous stress-creep strain curves as functions of sodium-exposure time and temperature. The low-cycle fatigue data were used to obtain relationships between plastic strain range and cycles-to-failure based on the Coffin-Manson formalism and a damage-rate approach developed at ANL. An analysis of the cyclic stress-strain behavior of the materials showed that the strain-hardening rates for the sodium-exposed steels were larger than those for the annealed material. However, the sodium-exposed specimens showed significant softening, as evidenced by the lower stress at half the fatigue life. Microstructural information obtained from the different specimens suggests that crack initiation is more difficult in the long-term sodium-exposed specimens when compared with the solution-annealed material. Based on the expected carbon concentrations in LMFBR primary system sodium, moderate carburization of the austenitic stainless steels will not degrade the mechanical properties to a significant extent, and therefore, will not limit the performance of out-of-core components.
Date: September 1, 1977
Creator: Natesan, K.; Chopra, O.K.; Zeman, G.J.; Smith, D.L. & Kassner, T.F
Partner: UNT Libraries Government Documents Department

Influence of a simulated HTGR environment on the mechanical properties of a commercial Ni-Cr-Mo-Fe alloy (Hastelloy Alloy X)

Description: The influence of a simulated advanced-reactor helium environment, containing 500 ..mu..atm H/sub 2//50 ..mu..atm CH/sub 4//50 ..mu..atm CO/approx. 1 ..mu..atm H/sub 2/O, on the mechanical properties of two heats of Hastelloy Alloy X is discussed. Simultaneous exposures in air and controlled-impurity helium at temperatures in the range of 650/sup 0/ to 1000/sup 0/C for times of 3000 h or more were performed. A combination of tensile testing, Charpy V-notch impact toughness testing, and creep testing was used to study the effects of reactor helium/metal interactions on the mechanical behavior of this alloy. Carburization was identified as the primary corrosion phenomenon. Increasing exposure time and temperature were observed to increase the depth of carburization. The increase in carbon concentration in the carburized zone suppressed the additional formation of M/sub 6/C, which is observed in air-aged specimens, and resulted in the precipitation of M/sub 23/C/sub 6/, a chromium-rich carbide variant. The precipitation of M/sub 23/C/sub 6/ in the carburized zone occurred primarily along grain and twin boundaries; however, matrix precipitation was also observed, the degree of which depended on exposure temperature. Strength and impact toughness properties were found to be controlled primarily by thermal aging reactions, with only a small effect related to the carburization. Although tensile and creep ductilities were decreased as a result of carburization, substantial ductility remained. Variation was observed between the two heats, the finer-grained heat appearing to be weaker in the high-temperature creep tests and also possibly more susceptible to a loss of creep strength as a result of carburization.
Date: December 1, 1979
Creator: Li, C.C.; Johnson, W.R. & Thompson, L.D.
Partner: UNT Libraries Government Documents Department

Effects of methane concentration on the controlled-impurity helium corrosion behavior of selected HTGR structural materials

Description: The corrosion behavior of candidate structural alloys in a series of three simulated advanced gas-cooled reactor environments at 900/sup 0/C (1652/sup 0/F), with methane concentration varied, is discussed. The alloys investigated include three wrought alloys, Hastelloy X, Inconel 617, and Incoloy 800H; two cast superalloys, Rene 100 and IN 713; one centrifugally cast alloy, HK 40; and an oxide-dispersion-strengthened alloy, MA 754. Corrosion behavior was found to be strongly dependent upon both the alloy chemistry and the environment. Oxidation, carburization, and/or mixed behavior was observed depending upon the specific conditions. An equilibrium thermodynamics approach has been used to predict alloy behavior and explain observations relevant to the understanding of gas/metal interactions in reactor helium, which inherently contains small amounts of reactive impurity species. Carburization was identified as the primary corrosion phenomenon of concern, and detailed analyses were performed to determine the susceptibility and control of carburization reactions. The presence of alumina scales, containing small amounts of titanium, was found to be particularly effective in inhibiting carburization. Small variations in methane concentration have been shown to have a dramatic effect upon the oxidation potential and subsequent corrosion behavior of the alloy systems.
Date: December 1, 1979
Creator: Johnson, W.R. & Thompson, L.D.
Partner: UNT Libraries Government Documents Department

CO + H/sub 2/ reaction over nitrogen-modified iron catalysts. Quarterly technical progress report, October 1, 1983-December 30, 1983. [Denitriding of iron nitrides in both hydrogen and helium]

Description: The synthesis of epsilon-Fe/sub 2.7/N is confirmed by Moessbauer spectroscopy. Carburization of epsilon-iron nitride for 2.5 hours in 3H/sub 2//CO at 523 K starts the formation of a bulk structure similar to that seen during ..gamma..'-iron nitride carburization. Reaction of ..gamma..'-Fe/sub 4/N in 3CO/H/sub 2/ synthesis gas at 523 K shows a better bulk stability than reaction in 3H/sub 2//CO. Kinetic analysis of the product distribution at the higher CO ratio confirms greater activity and selectivity maintainance. The kinetics of denitriding in both He and H/sub 2/ was studied with a mass spectrometer. Extremely rapid nitrogen loss was observed from both ..gamma..'-Fe/sub 4/N and epsilon-Fe/sub 2.7/N catalysts in H/sub 2/ at 523 K. In both cases a initial exposure to H/sub 2/ produced a significant amount of NH/sub 3/ which we ascribe to an active surface species. Hydrogenation of the bulk continued with a slow rise to a maximum about 90 seconds after the introduction of H/sub 2/. The denitriding activity of the epsilon-Fe/sub 2.7/N catalyst was significantly higher than that of the ..gamma..'-Fe/sub 4/N catalyst. In contrast, the denitriding rate of epsilon-Fe/sub 2.7/N in He was significantly slower than that in H/sub 2/ until high temperatures (773K) were reached. An overall activation energy of 41.5 kcal/mol was obtained for this process. Comparison of the denitriding rate of virgin epsilon-Fe/sub 2.7/N in H/sub 2/ with that of the same nitride after five minutes of carburization during the hydrocarbon synthesis reaction indicates large differences in the overall rate. The carburized nitride was some 300 times less active to bulk hydrogenation than the virgin catalyst, which is indicative of significant changes in the first few layers of the nitride during the initial minutes of the synthesis reaction. 17 references, 5 figures.
Date: February 1, 1984
Creator: Delgass, W.N.
Partner: UNT Libraries Government Documents Department

Review of sodium effects on candidate materials for central receiver solar-thermal power systems

Description: Available information on the corrosion behavior and mechanical properties of structural materials in a high-temperature sodium environment has been reviewed to compile a data base for selection of materials for advanced central-receiver solar-power systems, for which sodium is being considered as a heat-transfer fluid and thermal-storage medium. Candidate materials for this application (e.g., Types 304, 316, and 321 stainless steel, Alloy 800, and Fe-2 1/4 Cr-1Mo and Fe-9Cr-1Mo ferritic steels) have been used in the construction of various components for liquid-metal fast-breeder reactors in this country and abroad with considerable success. Requirements for additional information on material properties in a sodium environment are identified. The additional data coupled with more quantitative deformation models, failure criteria, and component design rules will further reduce uncertainties in the assessment of performance limits and component reliability in large sodium heat-transport systems. 120 references.
Date: July 1, 1979
Creator: Chopra, O.K.; Wang, J.Y.N. & Natesan, K.
Partner: UNT Libraries Government Documents Department