Microstructure and Mechanical Properties of Ta-10W Alloy with Re and C Addition
With the development of aerospace,nuclear power,petrochemical engineering and other fields,stricter performance requirements are put forward for metal structural materials used at elevated temperature.Ta-based refractory alloys have good room temperature plasticity,but the high temperature mechanical properties of these alloys still need to be further improved.The appropriate amount of Re element has the effect of increasing the recrystallization temperature of the alloy,which significantly improves the high temperature strength without affecting the room temperature plasticity.The addition of a suitable amount of carbide can make the alloy form ahypo-eutectic lamellar structure,which significantly refined the grain and improved the high temperature strength of the alloy.However,too much ceramic phase will seriously deteriorate the room temperature plasticity of the alloy.Ta2C carbide ceramics show good metallicity and plasticity at room temperature,and the ceramic have good mechanical properties at high temperatures.Therefore,it is helpful to improve the high temperature mechanical properties of Ta-based refractory alloys by adding Re element or Ta2C carbide.In addition,there is no related research of Ta2C-reinforced alloys that has been done yet.In this work,the effect of Re(4.5％,mass fraction)and C(1％,mass fraction)on the microstructure and mechanical properties of Ta-10W(Ta:90％;W:10％;mass fraction)alloy was investigated.Ta,W and Re particles and TaC powders with a purity greater than 99.95％were used as raw materials,and the required alloy was prepared by vacuum arc melting.The test samples were prepared by electrical discharge machining(EDM)wire cutting and the microstructure and chemical composition of the samples were investigated using an XD30M optical metallographic microscope(OM)and a ZEISS SUPRA55 scanning electron microscope(SEM)equipped with an energy spectrometer(EDS).The crystal structure of the material was characterized by using a Bruker D8 X-ray diffractometer(XRD)and XRD data were quantitatively analyzed by Rietveld refinement method using GSAS software.The room temperature compressive properties were evaluated on a testing machine(GNT1000Y).The compression properties of the alloys at 1450 ℃ were tested by Gleeble3500 thermal simulation machine.The microstructure of Ta-10W alloy was body center cubic(bcc)single-phase solid solution,the fracture strain exceeded 24％at room temperature and the compressive yield strength was 190 MPa at 1450 ℃.Re(4.5％)had no significant effect on the phase structure of Ta-10W alloy,the fracture strain was 18.4％at room temperature,and the yield strength was 430 MPa at 1450 ℃,which was increased by 126％compared with Ta-10W alloy.The strength enhancement of Ta-10W-4.5Re alloys could be interpreted by the solid solution strengthening and fine grain strengthening effect.Moreover,the addition of Re(4.5％)increased the recrystallization temperature and melting point of the alloy,which improved the strength at high temperature of the alloy.When C(1％)was added to Ta-10W alloy,the microstructure of the alloy was fine and lamellar hypo-eutectic structure[bcc+(bcc+Ta2C)],and the needle-like precipitates were dispersedly distributed within the grains in the matrix,the fracture strain was 15.1％at room temperature,and the yield strength was 384 MPa at 1450 ℃.In Ta-10W-1C alloy,the primary carbide Ta2C was lamellar network structure in three dimensions,this structure strengthened the constraint between the reinforcement phase and the matrix.The lamellar ceramic phase became the core loadbearing body inside the material,and the matrix also had the function of bearing and transmitting loads.The metal matrix toughened the ceramic phase,and the lamellar ceramic enhanced the alloy's load-bearing capacity,both of which had strong synergistic strengthening effect.At the same time,the carbides promoted the nucleation of the bcc matrix phase and hindered the grain growth.The needle-like carbide particles dispersed and precipitated in the bcc matrix played a role in hindering the movement of dislocations.Thus,at room and high temperatures,the second phase of Ta2C strengthening could make an important contribution.Compared with Ta-10W-4.5Re alloy,Ta-10W-1C alloy had stronger softening resistance and better high temperature plasticity,which was because the three-dimensional lamellar structure had a stronger ability to withstand loads.The compressive fracture strain of Ta-10W-4.5Re and Ta-10W-1C alloys both exceeded 15％at room temperature,and their ultimate compressive strengths were both over 400 MPa at 1450 ℃,they had good high temperature strength and decent room temperature plasticity.Ta2C ceramics had unusual room temperature and high temperature plasticity,but the related research of Ta2C-reinforced was far from enough.If Ta2C ceramics were used as reinforcing phases in refractory high-entropy alloys,it was expected to prepare refractory alloys with better high-temperature mechanical properties.
refractory alloyceramic reinforcementhigh temperature mechanical propertiesmicrostructure
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