Development and optimization of carbide particle-reinforced titanium alloy matrix nanocomposites by selective laser melting

• Main Author: Tey Wei Shian
• Other Authors: Zhou Kun
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/77884
• Institution: Nanyang Technological University

Nanocomposites are composites that consist of at least one nanosized reinforcement phase. By reducing the reinforcement particle size from the micrometre to nanometre level, the mechanical properties of the nanocomposite can be significantly improved beyond that of conventional composites. However, nanocomposites are not widely used in industries due to the lack of adequate processing methods. In conventional processing methods, the nanosized reinforcement particles in the matrix experience large van der Waals forces due to their high specific surface area, causing uncontrolled agglomeration of the nanosized particles and resulting in an non-uniform distribution of reinforcement nanoparticles in the matrix material. Selective Laser Melting (SLM) is a recently developed additive manufacturing (AM) technology that can produce complex, fully dense and functional parts using digital files from a computer-aided software. SLM has shown success in printing nanocomposites with a homogeneous mixture of reinforcement nanoparticles in the matrix material. However, more research is required to better understand and control the microstructural development and mechanical properties of nanocomposites printed using SLM. In this project, tungsten carbide (WC) reinforced and molybdenum carbide (Mo2C) reinforced Ti-6Al-4V (Ti64) nanocomposites with nearly full density were successfully printed via selective laser melting starting from the mixture of microsized Ti64 and nanosized carbides. Different weight fractions of WC and Mo2C reinforcements ranging from 1 wt.% to 3wt.% were designed and optimized based on the microstructure and mechanical properties of the printed nanocomposite parts. Results show that as the addition of WC and Mo2C reinforcement particles increases, the amount of needle-like α’-Ti phase martensite decreases. The boundary of the melt pool also becomes more distinct as the reinforcement content increases. Precipitates ii of unreacted reinforcement material can be observed at the melt pool boundaries for samples of each reinforcement material. WC/Ti64 samples show up to 20.88% increase in tensile strength, while Mo2C/Ti64 samples show up to 16.42% increase in tensile strength. However, there is a significant decrease in strain as the weight fraction of reinforcement increases. Mo2C/Ti64 samples show a significant increase in microhardness of up to 22.64% (3 wt%), while WC/Ti64 samples show up to 12.39% improvement in microhardness (3 wt%). Samples of both reinforcement materials show a similar rate of decrease in fracture toughness with increased addition of reinforcement material. All samples show similar wettability properties, with water contact angle ranging from 70 ° to 90 °.