| W-Ni-Fe high density tungsten alloys have been fabricated by means of Liquid Phase Sintering(LPS) of Powder Metallurgy(P/M). The effect of the performance of raw powder and process parameter such as sintering time & temperature , heat treatment time & temperature on the plastication of tungsten alloys has been studied. At the same time, the effect of addition with Co, La, Ce element powder on the properties of alloys has been researched. The test samples have been tested and analyzed by means of materials tensile test machine, microhardness device, optical microscope, SEM, gas phase chromatogram instrument, X-ray optical electron energy spectrum and so on. The result showed that the effects of the performance of raw powder and process parameter such as sintering time & temperature on the plastication of alloys is by way of the effects on the microstructure of alloys, but heat treatment and addition is by way of variation of interface combination state of alloys.The finer raw powders have larger drive force than lager size powders in LPS, and this characteristics benefit for the reaction of solution- diffusion mechanism and densification of the compact is easily. The microstructure of sintering pieces is propitious to plastication.The 90W-7Ni-3Fe alloys sintering at 1500C, in 120min have the best properties, the elongation that is major parameter for plastication of alloys is 12%.The optimal heat treatment process of alloys is annealing at 1200C,in 120min, cooling quickly, in vacuum of 6.7 X 10-3 Pa. After heat treatment, the hydrogen content in the samples has decreased obviously, the diffusion between matrix and tungsten particles has carried though fully, the strength of interface between matrix and tungsten particles has increased, the microstructure of samples tend to circularity that benefit for plastic deformation, the elongation of the samples gets to above 23%. At the same time, the Ultimate Tensile Strength(UTS) has increased remarkably, the transcrystalline fracture of tungsten particles is the major fracture form in the SEM fracture photos.The element Co has very good soakage property to the alloys element Fe and Ni because of the lower melt point of Co and the outerlayer electron structure, so the combination strength of interface between matrix and tungsten particles in alloys with Co addition has increased further. Meanwhile, the sintering temperature of alloys has decreased, activated sintering has been realized and the diffusion in alloys has been increased, the edge of tungsten particles become smooth and this benefit plastic deformation, then the elongation of alloys gets to above 30%.The earth elements have stronger affinity to hydrogen, oxygen and sulfur than other elements. The hydrogen content in alloys has reduced further so as to lower the effect of hydrogen embrittlement; in addition, the oxygen content between matrix and tungsten particles has been lowered, the tungsten oxide film between matrix and tungsten particles has been removed. The result of test showed that the UTS and elongation of alloys have been improved.The microstructure of high density tungsten alloys consists of nearly spherical grains of body-centered cubic tungsten surrounded by a solidified face-centered cubic matrix phase containing Ni, Fe, and W. This alloys are typical two phase alloys. The first factor that effects on themechanical properties of alloys materials is interface combination force, and the second one is the relative content, distribution and configuration of two phase. Based on thinking about above factors, the component and process design for the tungsten alloys has been discussed on this paper by means of LPS of P/M.
|
PDF Full Text Request