Technical Paper: PIM International, Vol.3 No. 1 March 2009, pages 56-59, 1939 words

Author: Hao He, Yimin Li, Jia Lou and Jianguang Zhang

State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, China 

Abstract

In this work, the co-sintering compatibility between Fe2Ni and Fe2Ni with different amounts of Cr additions (Fe2NixCr, x=0.5, 1, 3) was studied. The intent is to manufacture functionally graded composites for applications that require a combination of toughness and wear resistance.

The densification, bond strength and microstructure of the composites were examined. It was found that the density and bond strength of the composites increase at first, and then decrease with increasing chromium content. Co-sintering significantly aids the densification of the Fe2NixCr side. The density of the composites is not uniform but graded from the Fe2Ni side to Fe2NixCr side. In all cases the interface is free of cracks. A transitional zone composed of granular pearlite and lamellar pearlite was clearly seen. The best results were found using Fe2Ni/Fe2Ni1Cr composition. Final parts had densities close to 96% and a bond strength of 289.9 Mpa.

Introduction

Metal injection moulding (MIM) has over the past decade established itself as a competitive manufacturing process for the production of small intricately shaped components [1]. Metal co-injection moulding (co-MIM), an enhancement of the conventional MIM process, has attracted growing attention in recent years because the process allows the integration of two dissimilar materials with different physical properties in a single production route [2, 3].

In this method, twin-barreled injection moulding machines equipped with different injection units are used, from which functionally graded composites having different structures can be easily manufactured. Such a component that has an interlocked structure is moulded by a machine having rotatable cavities and a core/shell structure (sandwich structure) by injection of two different feedstocks in subsequent stages through one gate, and a bi-layer structure by injection of two different feedstocks simultaneously through two different gates [4-6].

After debinding and sinter-densification, boundaries between the dissimilar materials will be replaced by solid bonding. Due to its ability to optimise component properties during moulding rather than by post-processing, co-MIM can be regarded as a potential manufacturing technology to meet the strong customer demand for efficient manufacturing methods of functionally graded composites.......

Further sections of this article include:

- Experimental
- Results and discussion

Figures and Tables:

Fig. 1 Schematic presentation of the mould used
Fig. 2 Relative density of Fe2Ni/Fe2NixCr composites
Fig. 3 Density of the samples cut by wire cutting machine
Fig. 4 Polished metallograph of Fe2Ni (top) / Fe2Ni3Cr (bottom) composite
Fig. 5 Etched microstructure of Fe2Ni (top) / Fe2Ni3Cr (bottom) composite (A: granular pearlite; B: lamellar pearlite)
Fig. 6 Amplified micrographs of the interface zone of the composite
(A: granular pearlite; B: lamellar pearlite)
Fig. 7 Concentration of Cr around the interface of Fe2Ni (right)/Fe2Ni3Cr (left)
Fig. 8 Variation of microhardness along the interface area of Fe2Ni/Fe2Ni3Cr

Table 1 Density and strength of components