The Performance Of Powder Metallurgy Molybdenum Alloy Forging And Microstructure Research

Molybdenum-Titanium-Zirconium alloy is a unique refractory metal combined with remarkable high-temperature strength,corrosion resistance and creep-resistance, high thermal conductivity, low coeffcient of thermal expansion, so that it has been widely used in electronic industries,metallurgies,aerospaces and nuclear reactor vessels. The conventional PM Mo-Ti-Zr alloys have the pores and cause the decrease of tensile strength and elongation,so the application of Mo-Ti-Zr alloys are limited.In order to increase the density and mechanical properties of PM Mo-Ti-Zr alloy, Mo-Ti-Zr alloy rods were prepared by cold isostatic pressed and high temperature sintered, and the high temperature sintering alloy rods were rotary forged.The influences of sintering temperature,rotary forging temperature,deformation amount,intermediate annealing time during the rotary forging process and annealing temperature on mechanical properties and microstructure of Mo-Ti-Zr alloy rods were investigated and the influences of the pores and the second phase particles were analysed,the results are as follows:(1) The increase of density and tensile strength of Mo-Ti-Zr alloy rods rotary forged decrease, the increase of hardness is obvious with increasing sintering temperature. Mo-Ti-Zr alloy rods sintered at 1800℃reach the max value, tensile strength is 650Mpa and elongation is 1.5%.The large grains of Mo-Ti-Zr alloy rods rotary forged easily merge and coarse and the scale of transgranular fracture increase with the increasing sintering temperature.(2) The density,hardness and tensile strength of Mo-Ti-Zr alloy rods rotary forged at 1200℃are higher than at 1400℃.The low carbon steel can reduce forging temperature and effectivly avoid the grains excessive growing.The density,hardness,tensile strength increase slowly with the increasing deformation amount. The density of Mo-Ti-Zr alloy rods reach 9.83g/cm3, hardness is 92.8HRB and tensile strength is 648Mpa after rotary forging to deformation amount of 27%. The fracture type of sintering Mo-Ti-Zr alloy rods is intergranular fracture,the fracture type of Mo-Ti-Zr alloy rods is changed to the mixing type of transgranular fracture and intergranular fracture after rotary forging to deformation amount of 27%.(3) The density and hardness increase slowly with the increasing intermediate annealing time during the rotary forging process. The tensile strength reach maximum at 40min.The hardness decrease slowly and tensile strength and elongation increase with increasing annealing temperature before 1000℃. Tensile strength and elongation reach maximum 669Mpa and 3.1% at 900℃.(4) The pores disappearance mechanics of Mo-Ti-Zr alloy rods is mainly physical metallurgical bonding of the surface of the pores closing at high temperature and three-dimensional compressive stress make the microcracks welded together. Though the second phase particles (Mo,Zr,Ti)xOy produce fine grain strengthening and dispersion strengthening,they avianize interface between molybdenum grains and result in fracture and recrystallization and the molybdenum grains growth occur and the mechanical properties decrease.