| W-Ni-Fe alloy is a typical refractory tungsten alloy,which was widely used in national defense,military and civil industry because of its high density and high hardness.With the development of modern society,the requirements for the performance of tungsten alloy are raised.Therefore,how to prepare high-performance tungsten alloy with low energy cost and high efficiency has become a research hotspot.Due to the larger difference of melting point and density between W and Ni,Fe,W-Ni-Fe refractory alloy was usually prepared by powder sintering,but the existing sintering technology has shortcomings for preparing high-performance refractory tungsten alloy,such as high sintering temperature or long sintering time,which cannot achieve the purpose of low energy cost and efficient preparation.Hot oscillating pressure,a pressure-assisted sintering technology based on hot pressure,which can convert static pressure into dynamic pressure.At present,this technology had made some research achievements in the preparation of high-performance materials,but the related research on hot oscillating pressure sintering was mainly focused on effect of sintering temperature and sintering time on material structure and property.As another important factor of sintering,pressure was found to have a great influence on improving the density of sintered alloys and shortening the sintering time.However,a little research had carried out the effect of pressure on sintering tungsten alloy,including hot oscillating pressure,which needs systematic and in-depth research.Based on this,W-Ni-Fe refractory alloy was prepared by hot oscillating pressing sintering under different oscillating pressures(median pressure and amplitude pressure).The effects of different oscillating pressures(median pressure and amplitude pressure)on the microstructure(grain size,density)and properties(hardness and corrosion resistance)of W-Ni-Fe refractory alloy were studied,and the relationship between sintering process,microstructure and properties was established.The sintering mechanism of high density and fine-grained W-Ni-Fe refractory alloy was studied,and its densification process was analyzed.Through the above research,the main results are as follows:(1)Increasing the median pressure could effectively increase alloy density and densification rate,refine grain size,increase the densification rate,the densification mechanism was dominated by plastic deformation,and thus improve the hardness and corrosion resistance.With the increase of median pressure,the relative density of W-Ni-Fe refractory alloy was gradually increased.When the median pressure was 40 MPa,and the density reached a maximum of 99.5%,while the grain size was only 3.8?m,an increase of only 22.6%compared with the original powder,and a decrease of about 14%compared with the median pressure of 20 MPa alloy.With the increase of the median pressure,the densification rate of the W-Ni-Fe refractory alloy was gradually increased,and the densification rate of the alloy at higher median pressure was always higher than that of the alloy at lower median pressure.Stress exponent of 3 at a higher median pressure indicates that the densification mechanism was plastic deformation.With the increase of the median pressure,the hardness and corrosion resistance of the W-Ni-Fe refractory alloy were also improved,among which the hardness of the alloy reached a maximum of 445.8 HV0.5 at the median pressure of 40 MPa,while the corrosion current was only 3.1×10-6 A/cm~2,which was 53.7%lower than the corrosion current of the alloy at the lowest median pressure.(2)Increasing the amplitude pressure can effectively improve the distribution of the binder phase of the W-Ni-Fe refractory alloy,decrease the porosity,reduce the grain growth rate,suppress the grain size,improve the properties of the sintered alloy,and increase the densification rate.With the increase of the amplitude pressure,the relative density of the W-Ni-Fe refractory alloy gradually increased,and the particle contiguity and the thickness of the bonding phase gradually decreased.When the amplitude pressure was 10 MPa,the density and grain size were 99.2%and 3.7?m,respectively,and the grain growth rate was only 1.12×10-15m~2s-1,the grain growth was significantly inhibited,the particle contiguity and the thickness of the bonding phase were 68%and0.43?m,respectively.With the increase of amplitude pressure,the densification rate of W-Ni-Fe refractory alloy was gradually increased,and the densification rate of alloy under higher amplitude pressure was always higher than that under lower amplitude pressure.With the increase of the amplitude pressure,the hardness and corrosion resistance of the W-Ni-Fe refractory alloy was also improved.When the amplitude pressure was 10 MPa,the alloy was exhibited the highest hardness of 454.7 HV0.5,while the corrosion current was only 5.09×10-6 A/cm~2,the corrosion current of the alloy was reduced by 9%compared with the lowest amplitude pressure. |
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