Preparation Of High Strength And High Toughness W(Ta,Nb) Solid Solutions And Its Sintering Diffusion Behavior With Ferronickel

Tungsten has the advantages of high melting point,high density,high strength and low coefficient of thermal expansion and it is suitable for military industry and advanced manufacturing.Tungsten is a refractory metal material with a typical body centered cubic structure.Due to the strong covalent orientation bonds between W and W and its non-planar dislocation core structure,the screw dislocation mobility is extremely poor,resulting in great intrinsic brittleness of pure tungsten,which severely restricts its further application.Therefore,in this paper,W（Ta,Nb）solid solutions were prepared by adding tantalum（Ta）and niobium（Nb）and sintered with ferronickel composite.The effects of tantalum and niobium on the microstructure,mechanical properties,strength and toughness of W（Ta,Nb）solid solutions,as well as the interfacial reaction between tungsten based solid solutions and ferronickel were investigated.W（Ta,Nb）solid solutions materials with high purity,high strength and high toughness were obtained.The microstructure evolution and element migration mechanism of the interfacial reaction between W（Ta,Nb）solid solutions and nickel iron have been revealed,which provided theoretical support for the preparation of new tungsten alloys.The main results achieved are as follows:（1）W-x Ta（x=10 wt.%～50 wt.%）alloys with different tantalum contents were successfully prepared by spark plasma sintering and arc melting.The influence of tantalum content changes on the microstructure evolution and properties of tungsten based solid solutions was analyzed.The compressive strength and compressive strain of W-Ta solid solutions are 1311 MPa and 16%,respectively.The strengthening and toughening mechanism after the addition of tantalum was revealed.The deformation mechanism after the addition of tantalum changed from mainly screw dislocation to a joint action of edge dislocation and screw dislocation.The mechanism of grain refinement of tungsten based solid solutions by tantalum content was also revealed.（2）W-30Ta-x Nb（x=0 wt.%～5 wt.%）solid solutions with different niobium contents were prepared by arc melting.The effects of trace niobium on the solutions,microstructure,structure,and mechanical properties of tungsten based solid solutions were revealed.After the addition of niobium,the structure of W-30Ta-Nb solid solutions was still single-phase BCC,lattice distortion and lattice constant increased.The hardness of W-30Ta-Nb solid solutions increased and then decreased,and the elastic modulus decreased gradually upon increasing the niobium content.The strength first increased and then decreased upon increasing the niobium content.The compressive strength and compressive strain of W-30Ta-Nb solid solutions are 1.7 GPa and 24%,respectively.（3）The strengthening and toughening mechanism of tantalum and niobium was revealed.The further improvement of strength and toughness is mainly due to niobium fine crystal strengthening,solid solution strengthening and dislocation multiplication.The compound addition of tantalum and niobium promoted the proliferation of dislocation in the deformation process of tungsten based solid solutions,constructed a large number of dislocation and greatly improved the yield strength.At the same time,the grain size of W-30Ta-Nb solid solutions decreased upon increasing the niobium content,which synergistically improved the strength and toughness of tungsten based solid solutions.（4）The mechanism of interfacial diffusion reaction between tungsten based solid solutions and ferronickel under different sintering processes was clarified.Temperature is a key factor affecting the progress of interfacial reaction.When the sintering temperature was higher than1200℃,the interfacial reaction was intense.A multi-layer interfacial reaction layer composed of Ni₂Ta,Ni₃Ta intermetallic compounds andγ-（Ni,Fe,W,Ta,Nb）solid solutions phases were formed between tungsten based solid solutions and ferronickel.Ni₃Ta intermetallic compound was the main interface product.Ni₃Ta gradually growed from needle like to lath like,and finally evolved into block like upon increasing the sintering temperature.185 Figures,12 Tables and 196 References...