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 μm compared with that of the GH3536 alloy (9.5 μm) 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 °C and 815 °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.