Improvement in tensile strength of GH3536-TiB2 composites fabricated by powder metallurgy

To further improve the tensile strength of the GH3536 alloy (Hastelloy X), the GH3536-1 wt%TiB2 composites were prepared successfully by powder metallurgy. The results show that numerous M3B2 and TiC particles precipitated in the GH3536-TiB2 composite system. Interestingly, M3B2 particles were distributed along the grain boundaries in the composites, while TiC particles were in-situ synthesized along the prior particle boundaries of the spherical GH3536 powders. In addition, the grain size of the composite matrix was decreased to 6.7 & mu;m compared with that of the GH3536 alloy (9.5 & mu;m) since the grain growth being hindered by numerous intergranular phases, which further caused the increase of twin boundary proportion (from 26.5% in the GH3536 alloy to 38.8% in the composites). Consequently, the yield strength of the prepared composites was improved to 361 MPa and 298 MPa, respectively, from 240 MPa and 200 MPa, representing a roughly 50% improvement over the GH3536 alloy at 700 degrees C and 815 degrees C. The improvement in high-temperature strength is mainly ascribed to grain refinement strengthening, twin strengthening, hetero-deformation-induced hardening, and the additional grain boundary strengthening effect induced by secondary phases.