Comparative Study on Mechanical Property and Fracture Behavior of Age-Hardened LM4 Monolithic Composites Reinforced with TiB2 and Si3N4

Abstract

The study aimed to compare and analyze the mechanical property and fracture behavior of LM4 composites reinforced with TiB2 (1–3 wt.%) and Si3N4 (1–3 wt.%) ceramic powders. A two-stage stir casting process was employed for the effective preparation of monolithic composites. To further enhance the mechanical properties of composites, a precipitation hardening treatment (both single (SSHT) and multistage (MSHT), followed by artificial aging at 100 and 200 °C) was conducted. From mechanical property tests, it was understood that in both the monolithic composites, the properties improved with an increase in wt.% of reinforcements, and composite samples subjected to MSHT + 100 °C aging treatment bested other treatments in terms of hardness and UTS values. Compared to as-cast LM4, there was a 32 and 150% increase in hardness and a 42 and 68% increase in UTS for as-cast and peak-aged (MSHT + 100 °C aging) LM4 + 3 wt.% TiB2 composites, respectively. Similarly, there was a 28 and 124% increase in hardness and a 34 and 54% increase in UTS for as-cast and peak-aged (MSHT + 100 °C aging) LM4 + 3 wt.% Si3N4 composites, respectively. Fracture analysis of the peak-aged composite samples confirmed the mixed mode of fracture in which brittle mode was dominating.