Functionally Graded Material Production and Characterization using the Vertical Separator Molding Technique and the Powder Metallurgy Method

Abstract

Functionally Graded Materials (FGMs) are advanced customized engineering materials that gradually and continuously change their composition. The current study investigated the production feasibility and some post-production mechanical/physical properties of B4C particle-reinforced (avg. 40µm) AA7075 matrix (avg. 60µm) FGM composites with the vertical separator molding technique using the high-temperature isostatic pressing powder metallurgy method. FGMs produced consist of three (0 – 30 – 60 wt. % B4C) and four (0 – 20 – 40 – 60 wt. % B4C) layers. The powders were mixed in a power blender mixer for 2h and were placed in the mold sections with a vertical separator. The lid was closed, and a pre-pressure of 10Mpa was applied. The FGM green sheet was transferred from the vertical separator mold to the hot work tool steel with a press. In this mold, FGMs were sintered at 560°C for 30 min under a pressure of 325MPa. Microstructural examinations did not reveal any separation or crack formation in the layer transition regions of the FGMs. In addition, a relatively homogeneous B4C reinforcing distribution was observed in the layers with a low reinforcement ratio (wt. 20% and 30%) compared to the other layers. The highest hardness was 170 HBN in one layer of the four-layer FGM containing 40% by weight B4C reinforcement. The highest transverse rupture strength was measured in the test performed from the region with the most reinforcement of the four-layer FGM at 482MPa.