Microstructure and Mechanical Properties of Vacuum Hot Pressed P/M Short Steel Fiber Reinforced Aluminum Matrix Composites

K Chandra,V Agarwala,S Jain

doi:10.1155/2014/312908

Abstract

Commercial purity aluminum powder of irregular shape and ligamental morphology having average particle size of 75 µm was blended with medium carbon steel short fibers having average diameter of 100 µm and maximum length up to 1000 µm. The green compacts of pure aluminum and reinforced compositions were hot-pressed in 10−3 torr vacuum, at 723 K, 773 K, and 823 K for 5, 10, and 15 min durations under 50 MPa axial stress on Gleeble 3800 simulator. Microstructures of the sintered composites have been studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The sintered compacts were characterized for densification behavior, hardness, and growth of FexAly reaction interface. Positive densification parameter was achieved for up to 10 wt.% reinforcement fraction. The maximum hardness of 51 Hv was achieved for 10 wt.% at 823 K for 15 min sintering time. The reaction interface was analysed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The reaction interface was found to be composed of Fe3Al, FeAl2, Fe2Al, Fe3Al, Fe4Al, Fe2Al5, and FeAl intermetallics. Growth of the reaction interface was diffusion-controlled which followed a nearly parabolic law with a rate constant of 1.41 × 10−12 m2 s−1 at 823 K.

Highlights

Powder metallurgical (P/M) processing is based on blending of matrix powders and reinforcing elements, secondary working operations like forging, extrusion and hot pressing [1, 2]
The mixture of aluminum with short steel fiber, designated as Al5SSF, Al10SSF, and Al15SSF, for respective weight fractions of reinforcement was blended in a horizontal tumble jar mill using ceramic balls of 16 mm diameter, with a ball to composite weight ratio of 1 : 1, to avoid agglomeration of fibers, while ensuring that the fiber aspect ratio was maintained; a uniform distribution was obtained after 2 h of milling at 80 rpm
Resistive heating was found to be more effective than traditional methods of heating as evident by the high rate constant of reaction at the fiber matrix interface

Summary

Introduction

Powder metallurgical (P/M) processing is based on blending of matrix powders and reinforcing elements (particles, platelets, or whiskers), secondary working operations like forging, extrusion and hot pressing [1, 2]. P/M methods offer the ability to modify the chemistry and retain control over the matrix-reinforcement interface. Plastic flow, and power-law creep have been identified as the dominant mechanisms for densification by hot isostatic pressing (HIP) sintering [8]. Vacuum hot pressing (VHP) is found to enhance the sintering rate and final density of the compact in solid-state sintering, by providing additional stress at elevated temperature, whilst avoiding sintering aids and special atmospheres. Several workers have pursued the continuous reinforcement of aluminum alloys by stainless steel or steel wires using liquid metallurgical processes, to offer a costcompetitive improvement in overall properties of monolithic aluminum alloys. Investigations have shown the formation and uncontrolled growth of a complex intermetallic reaction interface (RI) of type FexAly composed of Fe3Al, FeAl, FeAl2, Fe2Al5, and FeAl3 phases [9,10,11,12,13,14,15]

Methods

Results

Conclusion