In order to improve both fracture strength and resistance to embrittlement at low temperature, fine-grained sintered molybdenum alloys dispersed with fine TaC, TiC, ZrC or HfC particles of 0.4-1.6mol% were prepared by mechanical alloying (MA) and hot isostatic pressing (HIP). The mixtures of fine molybdenum powder with grains measuring 20nm in diameter and carbide particles prepared by MA, were sintered at 1570K for 10.8ks under 147MPa. The sintered alloys had relative densities of over 99% and grain sizes of 0.2-10μm. The low-temperature fracture strength and ductile-to-brittle transition temperature (DBTT) were evaluated by three-point bending test at 77K to 360K. The following results were obtained.
(1) The low-temperature fracture strength was increased and DBTT was decreased by dispersion of carbides in the sintered alloys prepared by MA and HIP.
(2) The sintered alloy dispersed with TaC has a high fracture strength of 1880MPa and a low DBTT of 156K.
(3) The sintered alloys were strengthened by carbide dispersion and grain refining, though the former effect is much effective.
(4) The intergranular fracture surface was predominant in the sintered alloy dispersed with TaC and pure-molybdenum, while the transgranular fracture surface was predominant in all other sintered alloys.