| In this paper,Mo-20Cu composite powder was prepared by chemical synthesis evaporation crystallization method.The solution was prepared by using ammonium tetramolybdate and copper nitrate powders.The molybdenum-copper composite precursor was prepared by optimizing the process parameters in an evaporative crystallizer.Then the precursor is dried,calcined,and reduced to complete the molybdenum-copper composite powder.The effects of evaporation and crystallization on the phases,morphology,and particle size of molybdenum-copper precursors were studied.In addition,the effects of hot-pressing sintering and pressureless sintering in H2 atmosphere on the microstructure and properties of molybdenum-copper composites were discussed.The results of evaporation and crystallization showed that the pH of the copper nitrate solution had a great influence on the phase composition and morphology of the molybdenum copper precursor,Stirring rate and heating power have no effect on the precursor phase,but have a greater influence on the powder mophology.With the increase of heating power,the precursor particles increase and grow irregularly.The increase of the stirring rate will lead to grain refinement,and the powder will appear agglomeration.Considering comprehensively,when the pH value is 3,the stirring rate is 500r/min and the heating power is 0.3kw.The precursor powder particles prepared by the method are regular in shape,uniform in size,and distributed in the form of rods.The precursor phases are both In addition to(NH4)2Cu(MoO4)2,CuMoO4N0.42H1.26·2.4H2O,there is also a small amount of(NH4)4Mo0.8O26,which is favorable for subsequent calcination and reduction processes.After the precursor was calcined at 500?,the powder consisted of CuMoO4 and MoO3,and then the two-step reduction of H2 at 500? and 900? respectively resulted in an ultra-fine Mo-Cu composite powder with an average size of 200-500nm,and the two-phase distribution of molybdenum and copper was uniform.It is a "coated type" powder in structure,and the powder has Excellent sintering properties.The prepared composite powder was sintered by hot pressing and pressureless sintering in H2 atmosphere.With the increase of sintering temperature,the amount of copper in the liquid phase increases,the continuity of the copper network in the structure is better,and the grain size also increases.After sintering at 1100? for 3.5 h,the density,hardness,bending strength and compressive yield strength of the composites were the best:95.7%,235.7HV,816MPa,and 770MPa,respectively.In the 1350?H2 atmosphere without pressure sintering for 2h,the density,hardness,bending strength and compressive yield strength of the composites reached the best 92.87%,198.5HV,964MPa and 482MPa,respectively.However,in these two sintering methods,the conductivity of the materials is not much different,which is 18.72MS/m and 17.9MS/m,respectively.However,when 0.7%Fe was added under the same sintering process,the microstructure and properties of the sintered body were improved because Fe and Mo formed a solid solution,and the solid strength enhanced the strength of the material.The hardness,bending strength,and compressive strength were 223.5HV,1074MPa,and 614MPa,respectively,but the addition of Fe increased the electrical resistance generated by the electron scattering of Mo and Cu,resulting in a decrease in the electrical conductivity of 16.5MS/m. |
PDF Full Text Request