Study On The Effect Of Alloy Elements On The Preparation Process,Microstructure And Properties Of Molybdenum Alloy

Molybdenum is a rare metal resource with great strategic significance.In order to improve the defects such as low strength and poor plasticity,molybdenum alloy is usually strengthened by adding other elements to improve its applicable range.At present,there are few studies on the effects of alloying elements on the properties of molybdenum alloys Chinese molybdenum production is not standardized,the production process is also relatively chaotic.The lack of core technology directly causes the lack of international competitiveness of Chinese molybdenum products.To improve this situation,the effects of different powder metallurgy processes parameters?cold pressure,sintering temperature,holding time?on the microstructure and properties of molybdenum alloys were studied by changing the preparation parameters of molybdenum alloys.By adding Cu,Ta and Nb alloy elements respectively,the influence of alloying elements and their addition amount on the microstructure and properties of molybdenum alloy was systematically studied.The strengthening mechanism of molybdenum alloy by Cu,Ta and Nb alloy elements was also expounded.The research indicates:The relationship between the blank density and cold pressure of doped molybdenum alloys prepared by unidirectional pressing is also applicable to the double logarithm theory of huang peiyun.With the increase of cold pressure,the density of the compact increases gradually,but its growth rate decreases gradually.In the sintering process of molybdenum alloy,the reasonable sintering process can effectively promote the smooth progress of the alloying process,and ensure that the liquid phase has a better wetting effect on Mo grain.Within the scope of the study,with the improvement of sintering process?sintering temperature,heat preservation time?,the mechanical properties of molybdenum alloy showed a trend of increased first and then decreased.In the alloying element,the liquid phase Cu can gradually fill the pores and bond the Mo phase at high temperature.When the sintering temperature is 1650?and the holding time is 1h,the Cu phase will completely wet the Mo phase.At this time,Cu formed a uniform network structure among Mo grains,which had a strong bonding effect on Mo skeleton.Ta and Nb elements were gradually completely solid dissolved in the matrix Mo,and the stress field generated by lattice distortion has gradually maximized the hindering effect on dislocation motion,which has a strengthening effect on the matrix of molybdenum alloy.The addition of alloying elements can effectively reduce the recrystallization temperature of pure molybdenum and improve the mechanical properties of molybdenum alloy.The addition of Cu element through liquid phase sintered wetting matrix Mo,compared with Ta,Nb elements can greatly improve the density of molybdenum alloy,improve the alloy plasticity and toughness.When the Cu content increased to 12%,the relative density of molybdenum alloy reached a maximum of 95.8%.When the Cu content continues to increase to 16%,the strength and elongation of the alloy are 335MPa and 11.78%,respectively,which are close to the maximum values.The addition of Ta and Nb elements can form replacement solid solution through solid solution in Mo,which can greatly strengthen the molybdenum matrix and improve the mechanical properties of molybdenum alloy.When the addition of Ta and Nb was 8%and 2%respectively,the tensile strength of molybdenum alloy was 320MPa and 335MPa,both close to the maximum value.As the addition of Ta and Nb continued to increase to 10%and 6%respectively,the hardness of molybdenum alloy reached the maximum values of 267.7HV and 238.7HV,which were nearly 34.2%and 19.6%higher than that of pure molybdenum,respectively.In addition,Ta and Nb elements can be properly added to form stable second phase oxides Ta₂O₅ and Nb₂O₅ by adsorption of oxygen atoms existing in the pores,which can purify the impurities in the alloy and effectively reduce the gas pressure in the pores,the pore shrinkage was promoted and the densification of molybdenum alloy was improved.However,the oxidation phase belongs to brittle phase,and the increase of Ta₂O₅ content causes the appearance of transgranular cleavage fracture in the fracture morphology of the alloy,which is not conducive to the plasticity of the alloy.The excessively high Ta and Nb rich oxide will cause the serious deviation of Ta and Nb elements in the alloy,which directly lead to the decline of the alloy's strength and toughness performance.