Molybdenum Alloy TZM Research Articles

Data reduction and uncertainty assessment of the direct pulse heating technique with both contact and radiance temperature measurements

This work presents a data reduction procedure of the direct pulse heating technique with both contact and radiance temperature measurements. The technique is applied for the measurement of thermophysical properties of electroconductive solids over a wide temperature range, i.e., from room temperature up to about 2300°C. Absolute and radiance temperatures of a tested material are measured by thermocouple and radiation thermometer, respectively and these and other experimental data are then reduced to the values of specific heat, specific electrical resistivity, hemispherical total emissivity and normal spectral emissivity of the tested material. The related data reduction and corresponding uncertainty assessment for each property is described in detail. An example of uncertainty assessment is given for the recent measurement of specific heat, specific electrical resistivity, hemispherical total emissivity and normal spectral emissivity at 900 nm of molybdenum alloy TZM specimens.

Microstructure and mechanical properties of molybdenum-titanium-zirconium-carbon alloy TZM processed via laser powder-bed fusion

Molybdenum, processed by laser powder-bed fusion (LPBF), is susceptible to hot cracking because segregated oxygen impurities significantly weaken grain boundaries through the formation of MoO2. The present study reports on the LPBF processing of the most important molybdenum alloy TZM, whose alloying elements—titanium, zirconium, and carbon—lead to particle and solid solution strengthening. Results of investigations into the resulting microstructure and mechanical properties when processing TZM by LPBF are presented. The alloying elements suppress the segregation of oxygen to the grain boundaries so that crack-free samples with a density of 99.7 ± 0.3% may be produced. The microstructure shows grains that are columnar due to epitaxial grain growth and a weak 〈111〉 fiber texture parallel to the building direction. Mo2C and ZrO2 particles with a size of <50 nm are precipitated in the grain interior. Oxygen is not only bound by ZrO2. Research has shown that the ternary molybdenum‑titanium carbide, which can be found in LPBF – TZM – as is the case with pressed/sintered TZM—can dissolve oxygen. While the bending strength is 591 ± 26 MPa for samples in which only pores with a diameter of <50 μm could be detected on the fracture surface, the bending strength drops to 267 ± 50 MPa for samples with defects of 400 μm. In both cases, the fracture mode is transgranular brittle.

Effect of notch parameters on the critical effective T-stress in elastic brittle fracture

The present work is aimed to investigate the effect of notch root radius ρ and angle of specimen on the critical effective T-stress. A notched plate made of molybdenum alloy TZM is considered and subjected to a tensile loading. In brittle materials, the tools derived from linear elastic fracture mechanics are applicable and the analysis was made according to a local approach defined by the volumetric method. Different values of notch root radius (ρ = 0.5, 1, 1.5, 2 mm) and angle ( = 0°, 15°, 30° and 45°) have been selected to conduct an analysis of the critical effective T-stress and the distribution of T-stress at the notch tip in brittle fracture. The effective T-stress Teff has been estimated as the average value of the T-stress distribution in the region ahead of the notch tip at the effective distance Xeff. The obtained results showed that the variation of radius affects strongly the critical effective T-stress, while the variation of angle gives a very small change in values of critical effective T-stress.

A new system for sodium flux growth of bulk GaN. Part I: System development

Though several methods exist to produce bulk crystals of gallium nitride (GaN), none have been commercialized on a large scale. The sodium flux method, which involves precipitation of GaN from a sodium–gallium melt supersaturated with nitrogen, offers potentially lower cost production due to relatively mild process conditions while maintaining high crystal quality. We successfully developed a novel apparatus for conducting crystal growth of bulk GaN using the sodium flux method which has advantages with respect to prior reports. A key task was to prevent sodium loss or migration from the growth environment while permitting N2 to access the growing crystal. We accomplished this by implementing a reflux condensing stem along with a reusable capsule containing a hermetic seal. The reflux condensing stem also enabled direct monitoring of the melt temperature, which has not been previously reported for the sodium flux method. Furthermore, we identified and utilized molybdenum and the molybdenum alloy TZM as a material capable of directly containing the corrosive sodium–gallium melt. This allowed implementation of a crucible-free system, which may improve process control and potentially lower crystal impurity levels. Nucleation and growth of parasitic GaN (“PolyGaN”) on non-seed surfaces occurred in early designs. However, the addition of carbon in later designs suppressed PolyGaN formation and allowed growth of single crystal GaN. Growth rates for the (0001) Ga face (+c-plane) were up to 14µm/h while X-ray omega rocking (ω-XRC) curve full width half-max values were 731″ for crystals grown using a later system design. Oxygen levels were high, >1019 atoms/cm3, possibly due to reactor cleaning and handling procedures.

Finite element analysis of the high-temperature creep deformation of a TZM heavy duty charge carrier

Due to its outstanding combination of properties, e.g. high electrical and thermal conductivity, low coefficient of thermal expansion and high rupture as well as high creep strength, the molybdenum alloy TZM is widely used in high-temperature applications. The creep deformation behavior due to transient thermal and charge-induced mechanical loading of a TZM heavy duty charge carrier for a high-temperature sintering furnace, is analyzed numerically with the ABAQUS finite element package. All structural parts of the assembly of the sheet-based charge carrier including joining elements such as screws and rivets are modeled. The creep behavior of the refractory metal components is accounted for by a rate-dependent constitutive material model which takes into account both the dislocation- as well as the diffusion-based regime. The fully coupled thermo-mechanical analysis safely detects failure-prone locations, and allows design improvements prior to the physical realization of assembly prototypes.

Brazing a Graphite Composite to Molybdenum Alloy TZM Using Active Copper-Based Filler Metals with Chromium Additive

Brazing a Graphite Composite to Molybdenum Alloy TZM Using Active Copper-Based Filler Metals with Chromium Additive

Thixocasting combination spanners using stainless steel X39CrMo17

Forging is state-of-the-art for producing hand tools on an industrial scale. Due to high demands on the stiffness and the fracture toughness, high-strength forging steels were used to provide cavity-free components with high mechanical load capacity. Moreover, forging is a cost-effective mass production process but, in spite of all its advantages, it has its limitations, e.g. in the freedom of designs. However, because of the extreme thermal loading (particularly with regard to permanent moulds) and the frequently unavoidable casting defects, hand tools are not cast. By means of thixocasting steel, technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging. Through near-net shape production, manufacturing steps and costs can be reduced. Furthermore, steels, which are difficult to forge but nonetheless have high potential for specific applications (such as high strength or corrosion resistant steels), can also be processed. In cooperation with industrial partners, X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast. Forming dies were designed and optimized by simulation, the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys. The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al 2O 3 protective coatings by plasma-enhanced chemical vapor deposition (PECVD). During the experiments, combination spanners were successfully cast in the semi-solid state. Cast parts were heat-treated to enhance the toughness of components, which was subsequently measured by a standardized torque test. Moreover, a hypothetical approach of a possible, industrial batch process was carried out using the simulation software MAGMAsoft.

Thixocasting Steel Hand Tools using Al2O3-coated Steel and Molybdenum Dies

Forging is state-of-the-art for producing hand tools on an industrial scale. Due to high demands on the stiffness and the fracture toughness, high-strength forging steels are used to provide cavity-free components with high mechanical load capacity. Moreover, forging is a cost-effective mass production process but, in spite of all its advantages, it has its limitations, e.g. in the freedom of designs. However, because of the extreme thermal loading (particularly with regard to permanent moulds) and the frequently unavoidable casting defects, hand tools are not cast. By means of thixocasting steel, technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging. Through near-net shape production, manufacturing steps and costs can be reduced. Furthermore, steels, which are difficult to forge but nonetheless have high potential for specific applications (such as high strength or corrosion resistant steels), can also be processed. In cooperation with industrial partners, X39CrMo17 stainless steel size 17 combination spanners were thixocast. Forming dies were designed and optimized by simulation, the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys. The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition (PECVD). During the experiments, combination spanners were successfully cast in the semi-solid state. Cast parts were heat-treated to enhance the components' toughness, which was subsequently measured by Charpy impact and tensile tests.

High temperature deformation behavior of the molybdenum alloy TZM

The molybdenum alloy TZM (Mo-0.5wt%Ti-0.08wt%Zr) is a commonly used constructional material for high-temperature applications. It is well known that molybdenum and its alloys develop a distinct subgrain structure and texture during hot deformation. These microstructural aspects have a significant effect on strength at elevated temperatures. It was observed that with proceeding primary recrystallization and therefore with disappearance of subgrains the yield strength drops almost to the level of pure molybdenum. The aim of the present work was to investigate and describe the strain hardening of hot deformed TZM on a microstructural basis. For this purpose sintered and prerolled TZM rods were recrystallized and each of them deformed to a specific degree of deformation afterwards. Especially the evolution of disorientation distributions was analyzed by electron backscattering diffraction (EBSD) and used to describe the work hardening effect. The yield strength was determined by tensile tests between room temperature and 1473 K. By analyzing disorientation profiles the formation and evolution of geometrically necessary and incidental dislocation boundaries could be observed. A model developed by Pantleon was used to describe the work hardening of TZM.

Evolution of Microstructure during Hot Deformation of the PM Molybdenum Alloy TZM

The molybdenum alloy TZM (Mo-0.5wt%Ti-0.08wt%Zr) is a commonly used structural material for high temperature applications. For these purposes a high strength at elevated temperatures and also a sufficient ductility at room temperature are being aimed. Preceding investigations revealed the existence of subgrains in hot deformed TZM. It was observed that with proceeding primary recrystallization and therefore with disappearance of subgrains the yield strength drops almost to a level of pure molybdenum. It is being assumed that the existence of a dislocation substructure has a pronounced effect on the yield strength of TZM. The aim of the present study was to evaluate the subgrain and texture formation and also to estimate the dislocation arrangement within subgrains during hot deformation. Hence, TZM rods were rolled to different degrees of deformation at a temperature above 0.5 Tm. The microstructure of the initial material was fully recrystallized. Texture formation, misorientation distributions and subgrain sizes were analyzed by electron backscattering diffraction (EBSD). Mechanical properties were characterized by tensile tests at room temperature and up to 1200°C. It was revealed, that with increasing degree of deformation a distinct substructure forms and therefore yield strength rises. Consequently, the misorientation between adjacent subgrains increases, their size decreases and a &lt;110&gt; fibre texture develops. To estimate the influence of texture on strength of TZM the Taylor factors are calculated from EBSD data.

Hardening mechanisms and recrystallization behaviour of several molybdenum alloys

The present study describes the effect of thermomechanical treatments on the microstructure of molybdenum–titanium and the molybdenum alloy TZM (0.5 wt.% Ti, 0.08 wt.% Zr). These alloys were processed by a powder metallurgical route including extensive rolling at temperatures above 1200 °C achieving deformation degrees of 2.87 (logarithmic). The alloys exhibit a distinct increase in yield stress without decreasing elongation at fracture. To study the recrystallization behaviour, several samples were annealed at temperatures between 1100 °C and 1600 °C for 15 min until 6 h. The microstructure was examined by scanning electron microscopy (SEM), electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). Strain rate controlled tensile tests and Vickers hardness measurements are used to determine the mechanical properties. In both alloys a distinct substructure containing subgrains is formed during deformation. A kind of (sub)grain refinement was considered to be responsible for hardening. Present particles are able to raise the recrystallization temperature and thus sustain the grain size effects even at working temperatures above 1200 °C.

Manufacturing and Testing of Actively Cooled Test Limiters for TEXTOR Made of an LPPS Tungsten-Coated TZM Heat Sink

To investigate the erosion and redeposition phenomena of fusion-related materials under stationary conditions, actively cooled test limiters were developed for the Tokamak Experiment for Technology Oriented Research (TEXTOR). The test limiters allow experiments under stationary conditions within a plasma pulse length of 10 s. Heat loads of typically 10 MW/m2 are removed by pressurized water; the volume flow is 10 m3/h, the pressure is 15 bar, and the minimum coefficient of heat transfer is nearly 70 000 W/m2·K. The limiters were manufactured as low-pressure plasma-spraying thermally sprayed tungsten-coated heat sinks made of the molybdenum alloy TZM. The required properties of the tungsten coating were developed by the use of a statistically based optimization routine. Optimized, actively cooled limiters were successfully tested in Forschungszentrum Jülich’s Material Research Ion Beam Test Facility (MARION) with hydrogen beams. Maximum heat loads of up to ~17 MW/m2 were applied without any failure of either the heat sink or the cooling system. The steady state of the surface temperature was measured within 2 s. Analytical and numerical models describing the effects of heat load distribution and spatial temperatures were found to be in excellent agreement with numerical predictions. In an additional experiment, loss of coolant was simulated. Transition boiling was generated, and after repeated heat loads higher than 10 MW/m2, cavitational damage of the heat sink occurred. Concerning the material selection for heat sinks of hypervapotrons and other cooling systems based on enhanced boiling of the cooling liquid, this result might be of special interest.

Activation of TZM and stainless steel divertor materials in the NET fusion machine

This paper presents the results of the activation and decay heat calculations for the divertor plate materials of the Next European Torus (NET). The basic option assessed enables molybdenum alloy TZM and AISI 316L as material for divertor cooling channels. Burn time, effective irradiation time history, and fluence dependence on activation, decay heat, and contact dose is assessed. Impact of the material impurity level on the radioactive inventory is also investigated. The ANITA code is used, with updated cross sections and decay data libraries based on EFF-2 and EAF-3 evaluation files. The flux-weighted spectrum provided by XSDRNPM or ANISN 1-D codes has been used. The real NET geometry was modelled with the 3-D MCNP Monte Carlo neutron transport code.

Neutron Irradiation Damage and Void Lattice Formation in a Molybdenum Alloy TZM

Molybdenum alloys are candidate materials for high heat flux components of fusion reactors. In order to study the neutron irradiation damage at high fluence levels, disks of the molybdenum alloy TZM that had been stress relieved at 1199 K for 0.9 ks were irradiated in the FFTF/MOTA at 679, 793 and 873 K to a neutron fluence of 9.6×10 26 n/m 2 (E n >0.1 MeV). Defect microstructures were observed by transmission electron microscopy. Dislocation structures consisted of isolated loops, aggregated loops (rafts) and elongated dislocations. The size of the loops increased with the irradiation tempetature. The levels of void swelling were 0.68 and 1.6% at 793 and 873 K, respectively

Performance of plasma sprayed B 4C coatings under high heat loads

In order to investigate the behaviour of B 4C coatings under thermal loading, a variety of substrates (fine grain graphite, carbon-carbon composite and the molybdenum alloy TZM) was covered with a coating of B 4C by low pressure plasma spray in an inert gas atmosphere. The thickness of the coating was varied between 125 and 250 μm. Mechanical tests proved good adhesion of the B 4C layer on all substrates. Tiles of the coated materials, 50 × 50 mm 2 and 50 × 25 mm 2 in size, were then exposed to high thermal fluxes in an ion beam test facility. The power densities applied on the specimens was varied between 3 and 10.5 MW/m 2 at pulse lengths up to 10 s (passively cooled specimens only). During thermal loading the surface temperature of the specimens was registered by means of optical pyrometers. Additionally, surface modifications of the specimens were observed with a video camera, and each pulse was recorded on tape. The results showed that already at surface temperatures below 2000°C crack formation in the B 4C coating and delamination occurred in particular for thick coatings (approximately 250 μm in thickness). On graphite substrates no melting of the B 4C-layer was observed up to more than 2100°C (melting temperature of B 4C ≈ 2400°C).

Crack propagation tests of first wall materials by cyclic irradiation with an electron beam

In this study, cyclic high heat flux beam irradiation tests were performed for clarifying the crack propagation mechanisms of type 316 austenitic stainless steel and molybdenum alloy TZM. In the experiments, a surface-cracked plate specimen was set in a vacuum chamber in a specimen jig which was connected to a load-cell. And a pulsed electron beam was used to simulate the high heat flux of a fusion reactor. The electron beam has a peak value of 12–20 MW/m 2 and 0.5 s operation time in every 30 s. After specified cycles of irradiation, the specimen was fractured by mechanical fatigue load. In all 316SS and some TZM specimens, thermal fatigue crack propagation was observed. To evaluate such a fatigue crack growth behavior only in 316SS, non-linear fracture mechanics analyses were performed based on finite element analysis. And these results were correlated with the non-linear fracture mechanics parameter.

Brazing of Titanium-Vapor-Coated Silicon Nitride

A technique for brazing Si{sub 3}N{sub 4} with metallic alloys was evaluated. The process involved vapor coating the ceramic with a 1.0-{mu}-thick layer of titanium before the brazing operation. The coating improved wetting of the Si{sub 3}N{sub 4} surfaces to the extent that strong bonding between the solidified braze filler metal and the ceramic occurred. Braze joints of Si{sub 3}N{sub 4} were made with Ag-Cu, Au-Ni, and Au-Ni-Pd alloys at temperatures of 790{degree}, 970{degree}, and 1,130{degree}C. Silicon nitride specimens were also brazed with a Ag-Cu alloy to the molybdenum alloy TZM, titanium, and A286 steel at 790{degree}C. Residual stresses resulting from mismatch of thermal expansion coefficients between the Si{sub 3}N{sub 4} and the metals caused all of the ceramic-to-metal joints to spontaneously crack in the Si{sub 3}N{sub 4} upon cooling from the brazing temperature.

Structure and properties of high energy, high rate consolidated molybdenum alloy TZM

Powders of molybdenum alloy TZM, prepared using the plasma rotating electrode process (PREP), were consolidated using high energy, high rate (HEHR) resistance sintering. The power source was a 10 MJ homopolar generator which provided power densities up to 9000 J g −1 over a duration less than 3 s. The effects of power density and electrode pressure were studied relative to product density. Inhomogeneity of densification was observed both axially and to a lesser degree radially. Tensile properties are equivalent to those of PREP powder hot isostatically pressed at 1600 °C. Fractographic examination revealed a transparticle, transgranular cleavage fracture mode. A detailed analysis was undertaken of second-phase precipitates formed during HEHR consolidation. Zirconia was present in starting powders and was unaffected by HEHR processing. Intragranular cubic TiC precipitated as stable 0.5 μm particles. Hexagonal Mo 2C precipitated on grain boundaries and ranged in size between 0.3 and 1 μm.

Void swelling in the molybdenum alloy TZM irradiated to high fluence

Microstructural development and density change measurements are reported for TZM, a commercial molybdenum base alloy, following fast neutron irradiation in EBR-II to high fluence over the temperature range 400 to 650°C. Uniformly distributed voids arrayed in a lattice and constituting 3% swelling were observed following irradiation at 650°C to 1.47 × 10 23 n/cm 2 ( E > 0.1 MeV) (53 dpa). Nonuniformly distributed rafts of voids in lattice arrays were observed following irradiation at 540°C to 1.36 × 10 23 n/cm 2. Void swelling was not resolved following irradiation at 425°C to 1.22 × 10 23 n/cm 2. Void swelling measurements corroborated density change results which showed peak void swelling behavior saturating at 590°C. Two mechanisms for the behavior observed are considered; the first is based on an apparent maximum void size of 10 nm which leads to void rafting and eventually to void swelling saturation. Saturation is predicted only after 10 24 n/cm 2 (360 dpa) with 20% swelling possible. The second mechanism considers the effect of a developing void lattice on dislocation dynamics.

Reaction of molybdenum and molybdenum-base alloy with sintered Li 2O pellets

The reaction of sintered lithium oxide (Li 2O) pellets with molybdenum and molybdenum-base alloy TZM has been studied in the temperature range 800–1100 °C for a constant reaction period of 100 h under a dynamic vacuum. The reaction proceeded measurably at about 950°C and appreciably above 1000°C. Metallographic and X-ray diffraction analyses indicated that a reaction product scale was formed at the interface and the scale consisted mainly of Li 4MoO 5. TZM showed slightly higher reactivity compared to molybdenum.