Characterization of TiC/316L composite powders produced by mechanical alloying method

This study aims to produce TiC/316L composite powders at different reinforcement ratios (0, 1, 3, 10 wt. %) and milling times (0, 1, 3, 5, 7 and 10 hours) by the mechanical alloying method and determine their suitability for powder metallurgical methods. The morphological characterization of the powders was carried out using SEM analysis. While the spherical shape of the powders is preserved their form during short milling times, the spherical shape has turned into a flake structure with increasing milling time. Flake powders, 40 µm average particle size with a thickness of 200-300 nm, were obtained at 5-7 hours milling time due to cold welding and plastic deformation effect. After 10 hours milling, it was found that small and irregular particle formation increased in all powder group because of excessive hardening mechanism. The crystallographic characterization of the milled powders was analyzed using the XRD method. Moreover, the average crystallite size, lattice micro-strain and, dislocation density of the milled powders have assessed by XRD data. As a result of increased milling time and reinforcement ratio; crystallite size decreased, lattice strain and dislocation density values increased. Among all groups; the lowest crystallite size (8 nm), the highest lattice micro-strain (1.01%) and the highest dislocation density (13.55 * 1015 lines/m2) were obtained in 3 wt. % TiC reinforced, and 10 hours milled powders. When X-ray diffraction patterns were examined, it was observed that 3 hours milling time was sufficient for a homogenous distribution of TiC particles into the Fe matrix. After the crystallographic characterization of the powders, the microhardness values were evaluated and, as expected, the highest hardness value was obtained in 10 hours milled and 10 wt. % TiC reinforced powder group (1082 HV). Besides, these powders, which can be used as raw materials in the powder injection molding method, were brought into feedstock with the help of a binder. Then rheological characterization was fulfilled to determine injection moldability. A simple linear regression analysis was performed on the shear stress and shear rate data obtained as a result of rheology experiments and then flow behavior indexes of feedstocks were obtained. It was observed all the unmilled (as-received or pre-mixed for 3 minutes) powders exhibited suitable characteristic properties for injection molding. However, the flow properties of the powders adversely affected, especially after pulsed powder formation. As a result of the decreased powder size after the maximum milling time (10h), it was monitored that milled powders exhibited similar flow characteristics behavior as unmilled powders. Consequently; composite powders were produced and characterized according to powder injection molding feedstock. Also, when the literature survey was examined, it was deduced that these composite powders are suitable for the conventional cold-hot press production and modern additive manufacturing methods.