Densification and grain growth during isothermal sintering of Mo and mechanically alloyed Mo–TZM

Mo–Zr and Mo–Ti alloy were fabricated by adding alloying element Zr, Ti in molybdenum via powder metallurgy process. The effect of Zr, Ti alloying elements on the tensile strength and microstructure of molybdenum are investigated. Two types of alloying additives are used: one is elemental powder of Zr or Ti; the other is their respective hydride powders, TiH2 or ZrH2. The experimental results show that the formed Mo–Zr, Mo–Ti alloy possess much higher mechanical properties than pure sintered molybdenum. The tensile strength of Mo–Zr alloy is more affected by adding elemental Zr powder than ZrH2 powder, the optimal tensile strength is obtained with addition of 0.1 wt% Zr, most of Zr forms Zr-oxide existed both inside the grain and at the grain boundaries, while very little Zr diffuses into the Mo matrix. Meanwhile, for Mo–Ti alloy, the tensile strength is more influenced by addition of TiH2 powder than elemental Ti powder, the tensile strength is optimized at the content of 0.8 wt% TiH2, some Ti diffuses into molybdenum and forms Mo–Ti solid solution and some forms as MoxTiyOz oxide particles uniformly distributed at the grain boundaries.

Effect of alloying elements Ti, Zr on the property and microstructure of molybdenum

Hot deformation behaviour of Mo-TZM and understanding the restoration processes involved

Effect of filler on the oxidation protective ability of MoSi2 coating for Mo substrate by halide activated pack cementation

Titanium, zirconium and molybdenum (TZM) alloy with different amounts of rare earth lanthanum oxide was prepared by powder metallurgy into 0.5 mm thick sheets. The effects of the La2O3 content on recrystallization temperature and mechanical properties of the TZM alloy were studied. La2O3 increased the recrystallization and recovery temperature of the TZM alloy and increased its tensile strength and elongation.

La2O3 effects on TZM alloy recovery, recrystallization and mechanical properties

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.

Hardening mechanisms and recrystallization behaviour of several molybdenum alloys

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 fibre texture develops. To estimate the influence of texture on strength of TZM the Taylor factors are calculated from EBSD data.

T. Mrotzek

Papers

Hardening mechanisms and recrystallization behaviour of several molybdenum alloys

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