Fracture Toughness of 6.4 Mm (0.25 Inch) Arc-Cast Molobdenum and Molybdenum-Tzm Plate at Room Temperature and 300 Degrees C Page: 2 of 11
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Summary
The fracture toughness of 6.4 mm (0.25 inch) low carbon arc-cast (LCAC) molybdenum and arc-cast
molybdenum-TZM alloy plate were measured at room temperature and 3000C using compact tension
specimens. The effect of crack plane orientation (longitudinal vs. transverse) and annealing practice
(stress-relieved vs. recrystallized) were evaluated. Depending upon the test temperature either a
standard Kc or a J-integral analysis was used to obtain the toughness value. At room temperature,
regardless of alloy, orientation, or microstructure, fracture toughness values between 15 and 22 MPa
m' (14 and 20 ksi in') were measured. These Kc values were consistent with measurements by
other authors. Increasing temperature improves the toughness, due to the fact that one takes
advantage of the ductile-brittle transition behavior of molybdenum. At 3000C, the fracture toughness
of recrystallized LCAC and arc-cast TZM molybdenum were also similar at approximately 64 MPa m'
(58 ksi in'). In the stress-relieved condition, however, the toughness of arc-cast TZM (91 MPa mA / 83
ksi iny') was higher than that of the LCAC molybdenum (74 MPa m7 / 67 ksi in').
Introduction
Background: Brittle failure analysis has become a common consideration in the design of many
structures. As a result, fracture toughness properties necessary to conduct brittle fracture analysis of
many common materials such as iron, aluminum and titanium alloys have been well characterized.
Relatively little effort has been devoted to the characterization of the fracture toughness of
molybdenum and molybdenum alloys. Because molybdenum's ductile-to-brittle transition temperature
(DBTT) is typically within approximately 100*C of room temperature, fracture - critical components
have not typically used molybdenum in this temperature range. Electronic heat sinks, for example,
rely on the thermal expansion and conductivity of the material, but do not include fracture
considerations in component design. Likewise, the high-temperature applications for molybdenum
and its alloys (heat treating furnaces, glass-melting furnace components, e.g.), concern themselves
more with long-term creep behavior than with fracture resistance.
In order, for molybdenum and molybdenum alloys to be considered for applications that must exhibit
fracture resistance, it is necessary to characterize the toughness of the material. The temperature
range between ambient and 12000C forms the region of most interest with respect to toughness. It is
in this region that components such as forging dies, metalworking tooling, and furnace structural parts
must operate, and in this range where additional characterization of fracture toughness must be
performed.
Prior Work: A few authors have investigated the toughness of molybdenum and molybdenum alloys.
Measurements of toughness values were performed on pre-cracked bend bars of extruded arc-cast
molybdenum as early as 1963 (1). These measurements used thick cross-sections, and calculated
the energy of fracture. Other early work investigated sheet molybdenum and TZM alloy (2), employing
thin sheet specimens that frequently displayed plasticity. The state-of-the-art at this time did not
permit an appropriate stress-analysis solution for such tests. Furthermore the authors were unable to
fatigue pre-crack the pure molybdenum samples without fracture, and relied upon EDM machining to
produce notches in the specimens. More recently the fracture toughness of molybdenum rod was
measured (3). These investigators solved the pre-cracking problem by using compression -
compression fatigue, and obtained K0c values for the specimen geometries with which they worked.
In the preceding work, toughness measurements were obtained at ambient temperatures. Russian
investigators have measured the toughness of molybdenum to temperatures of about 5000C (4,5), as
have German investigators (6). However there is no data on the fracture toughness of molybdenum
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Shields, J. A., Jr.; Lipetzky, P. & Mueller, A. J. Fracture Toughness of 6.4 Mm (0.25 Inch) Arc-Cast Molobdenum and Molybdenum-Tzm Plate at Room Temperature and 300 Degrees C, article, April 11, 2001; West Mifflin, Pennsylvania. (https://digital.library.unt.edu/ark:/67531/metadc743116/m1/2/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.