Preparation And Properties Of High Specific Gravity W-Ni-Fe Alloy

High-specific gravity W-Ni-Fe alloys,also known as tungsten heavy alloys(WHAs),are widely used in the aviation,aerospace,defense and nuclear industries due to their high mechanical properties,good corrosion resistance,no radiation contamination and low coefficient of thermal expansion.To meet the increasingly demanding material performance requirements,reducing the sintering temperature and refining the grain are the most effective means of enhancing WHAs,and refining the powder can effectively reduce the sintering temperature.In this paper,nanocomposite powders were prepared by mechanical alloying method,and 90W-7Ni-3Fe(90W)and 93W-4.9Ni-2.1Fe(93W)were prepared by pressureless sintering at a temperature lower than the liquid phase sintering temperature(1465 ℃).The effect of temperature on the structure and properties of the alloys was investigated.In addition,the addition of carbides has a great effect on hindering the growth of W grains;therefore,the effect of carbide(HfC,ZrC)on the structural properties of 90 W was investigated using 90 W as the matrix.Finally,the influence of the reinforcing phase content on the evolution of the organization and properties of the alloy is investigated using ZrC,which has a better influence on the structure and properties,as a variable.Firstly,90 W and 93 W were prepared using nanocomposite powders prepared by powder metallurgy and sintered at 1200–1450 ℃.The grain sizes of WHAs were in the range of 1.74-6.72 μm,and it was found that the compressive yield strength of 93 W was higher than that of 90 W at different temperatures,while the strong plasticity matching effect was best for WHAs sintered at 1300 ℃ with densities around 98%.The yield strengths of 90 W and 93 W were 1498 MPa and 1555 MPa,respectively.It was shown that the yield strengths of the alloys were closely related to the microstructural parameters of the alloys,including the W-W contiguity,W grain size,matrix phase volume fraction,etc.When WHAs were compressively deformed,the softer matrix bonded phase was preferentially deformed,and the geometric must dislocations were gradually stored in the grain boundaries as well as in the matrix.Secondly,based on the fracture morphology and compression curves,90 W with higher plasticity and densities at the same temperature was selected as the matrix for carbide addition.The nanopowders added with 1wt.% HfC or 1wt.% ZrC were sintered at solid phase sintering temperatures of 1400 ℃ and 1450 ℃ and liquid phase sintering temperature of 1500 ℃.With the increase of sintering temperature,the grain size of W grains becomes coarser,and the grain refinement effect of ZrC is stronger than that of HfC at the same temperature,and the effect is more obvious with the increase of temperature.The density of 90 W sintered at 1400 ℃ is 98.3%,and the density decreases after adding carbide,especially the density of ZrC/90 W,which decreases more,to only 97.5%,and the yield strength of the alloy increases less at this temperature,1142 MPa for 90 W and only 1180 MPa for ZrC/90 W.This is because the diffusion of W at the solid-phase sintering temperature mainly relies on the surface free energy of the powder as the driving force,and the diffusion rate is extremely low,so the added carbide cannot have a better fixing effect.Therefore,the added carbide does not have a good fixing effect.Under liquid phase sintering,the diffusion of W is greatly enhanced by the mechanism of dissolution,diffusion and reprecipitation,and therefore,the carbide can play a better role in hindering the diffusion of W.Finally,in the study of the effect of ZrC content on the structural evolution and properties of 90 W,it was found that the grain refinement of 90 W increased with increasing ZrC content,and the inhomogeneous distribution of W grains increased,and the yield strength reached 861 MPa with 2wt.% ZrC addition,but the strain only reached 25%,and even holes were found in the fracture.Therefore,the addition of 1wt.% ZrC results in a better ZrC/90 W strength-plasticity match,and the reinforcement has no additional strengthening effect on the yield strength of 90 W,but is only related to the changed structure(W-W contiguity,W grain size)of the ZrC.