Effects of Ta C on microstructure and mechanical properties of coarse grained WC-9Co cemented carbides

Coarse grained WC-9Co cemented carbides with 0-1.0% TaC(mass fraction) were fabricated by HIP-sintering and gas quenching. The effects of TaC on the microstructures and mechanical properties were investigated using scanning electron microscopy(SEM), energy dispersive X-ray analysis(EDS), X-ray diffractometry(XRD) and mechanical properties tests. The results show that the maximum values of hardness and strength are HV 1124 and 2466 MPa respectively when 0.4% TaC is added. When the content of TaC is more than 0.6%, the grain size of WC is no longer affected by the amount of TaC, and(W,Ta)C occurs as well. Moreover, the strength and fracture toughness increase and the(Ta+W) content decreases with the increase of TaC content. The dependence of(Ta+W) content on the mechanical properties indicates that(Ta+W) content in Co should be decreased as low as possible to improve the mechanical properties of coarse grained WC-TaC-9Co cemented carbides with the microstructure of WC+γ two phase regions.

Room temperature tensile deformation behavior of a Ni-based superalloy with high W content

K416B Ni-based superalloy with high W content has good high temperature properties and low cost,which has a great development potential.To investigate the room temperature tensile property and the deformation feature of K416B superalloy,tensile testing at room temperature was carried out,and optical microscopy (OM),scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the deformation and damage mechanisms.Results show that the main room temperature tensile deformation features of the K416B nickel-based superalloy are dislocations slipping in the matrix and shearing into γ’ phase.The <110> super-dislocations shearing into γ’ phase can form the anti-phase boundary two coupled (a/2)<110> partial-dislocations or decompose into the configuration of two (a/3)<112> partial dislocations plus stacking fault.In the later stage of tensile testing,the slip-lines with different orientations are activated in the grain,causing the stress concentration in the regions of block carbide or the porosity,and cracks initiate and propagate along these regions.

Effect of W on formation and properties of precipitates in Ni-based superalloys

The formation and properties of precipitates in wrought Ni-based superalloys with different W contents during long-term exposure to high temperatures were investigated.The scanning electron microscope,transmission electron microscope,and chemical phase analysis were used to investigate the formation and properties of precipitates.It is found that with increasing W content,the quantity and thermal stability of MC carbide in Ni-based superalloys increased,while the quantity of M_(23)C_(6)carbides decreased.As the results show,W has a higher partition coefficient in γ'-and γ-matrix,and the addition of W promotes the precipitation of γ'phase.W content has no significant effect on the morphology,size,crystal structure,and coarsening rate of γ'precipitates.The influence of W content on high-temperature tensile and creep properties of the alloys was investigated.The results showed that W content has no obvious influence on the high-temperature yield strength,but the elongation and area reduction decreased significantly when the addition of W was more than 4 wt.%.Because of the similar volume fractions of γ'phase,the creep fracture strengths in the tested alloys with lower W concentrations were not significantly different after long-term exposure at 700℃.