Low-temperature Hot Pressing,Microstructure And Properties Of The W_f/W Matrix Composites

Tungsten(W)is regarded as the most favorable candidate for plasma facing material of nuclear fusion reactor,due to its high melting point,low sputtering yield and fine thermal conductivity.However,application of the polycrystalline W for the structural materials is limited by its brittleness,strengthening and toughening of W is required.Compared with the W matrix composites reinforced by second phase particles,such as oxide and carbide particles,W fiber(W_f)reinforced W(W_f/W)matrix composites can not only maintain the performance advantages of W,but also improve the fracture toughness and alleviate the brittleness of the W matrix to a great extent.Furthermore,preparation process of the W_f/W matrix composites could be simplified,and fabrication cost could be reduced too,employing the W_f reinforcement without any pretreatment.And thus,the W_f/W matrix composites have a great application potential.In this investigation,the W powder and the W_f of various sizes were used as raw materials to fabricate the W_f/W matrix composites of different W_f contents via hot Pressing(HPing)at 1550?for 1.5 h.Microstructure and properties of the W_f/W matrix composites were investigated to optimize the sizes and contents of raw materials.The HPed 20W_f/W matrix composites achieve the pseudo-ductile behavior at room temperature,indicating an improvement of damage tolerance of the composites in terms of interface debonding and pulling-out of the W_f,during fracture of the composites.Nonetheless,the W_f/W matrix composites fabricated have low densities,employing current sintering schedule,and the strengthening and toughening effect of W_f is actually not good.Next,micro-alloying technology was carried out by adding small amount of Ni into the W powder to achieve densification of the W_f/(W-Ni)matrix composites via HPing at low temperature.As increasing the sintering temperature(<1400?),the relative density,bending strength and fracture toughness of the W_f/(W-Ni)matrix composites of 0.27 wt%Ni increase monotonically.Whereas,the bending strength and fracture toughness of the composites decrease,as the sintering temperature is higher than1400?,attributing to severely coarsening of W grains in the composites.The10W_f/(W-0.27Ni)matrix composites HPed at 1400?have the relative density,bending strength and fracture toughness as high as 96%,274 MPa and 4.97 MPa·m^1/2,respectively.As the Ni content decreased,the relative density of W_f/(W-Ni)matrix composites HPed at 1400?decreases monotonically,while the bending strength increases due to refinement of the W grains.Compared with the 10W_f/(W-Ni)matrix composites by adding 0.27 and 0.1 wt%Ni,the 10W_f/(W-0.05Ni)matrix composites have a relative density of 91.6%,and micropores distribute along the W_f/W matrix interface,so,the interface debonding and pulling-out of the W_f is enhanced.As a result,the composites have the bending strength and fracture toughness up to 305 MPa and 5.5 MPa·m^1/2,respectively.As increasing the W_f content,the relative density and thermal conductivity(TC)of the W_f/(W-0.05Ni)matrix composites decrease slightly.The 20W_f/(W-0.05Ni)matrix composites possess high relative density and preferable microstructural uniformity.More importantly,the micropores distribute uniformly along the W_f/W matrix interface to achieve a moderate interfacial bonding strength.Consequently,the 20W_f/(W-0.05Ni)matrix composites have the optimal comprehensive properties,i.e.,the bending strength,fracture toughness and TC of 353 MPa,6.2 MPa·m^1/2 and 120.2 W/(m·K),respectively.