Elsevier

Intermetallics

Volume 18, Issue 5, May 2010, Pages 871-876
Intermetallics

Preparation, microstructure and tribological properties of Ni3Al intermetallic compound coating by laser cladding

https://doi.org/10.1016/j.intermet.2009.12.020Get rights and content

Abstract

Single Ni3Al intermetallic compound phase coating was successfully in-situ synthesized by laser cladding with preplaced Ni and Al mixed powders. The phase composition and microstructure of the Ni3Al coating were studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The effects of laser cladding parameters on the microstructure and tribological properties of the Ni3Al coating were investigated. It was found that the laser power density and energy density had a crucial influence on the microstructure and tribological properties of the Ni3Al coatings. The Ni3Al coating synthesized under the lower power density and energy density had a dense and fine microstructure as well as some excellent properties such as higher and homogeneous distribution microhardness, lower friction coefficient and wear rate.

Introduction

Ni3Al intermetallic compound exhibits excellent physical and mechanical properties, such as high melting temperature, high hardness, low density, and good corrosion and oxidation resistance at an elevated temperature [1]. In addition, the yield strength of Ni3Al increases with the increasing temperature up to about 900–1000 K [2]. These properties have made Ni3Al as an attractive high temperature structural material and corrosion resistant material for a range of engineering application, such as gas turbine hardware, high temperature dies and molds, cutting tools and heat treatment fixtures [3]. However, there are still many limitations in its application as engineering materials because of the extreme brittleness of polycrystalline Ni3Al at ambient temperature [4], [5], especially that the fabrication of Ni3Al by the conventional cast is difficult and costly due to its poor workability.

In recent years, a lot of novel methods were developed to fabricate the Ni3Al, such as self-propagating high-temperature synthesis (SHS) [6], [7], reactive rapid prototyping (RRP) [8], and laser processing [9], [10]. However, it is difficult to obtain high quality products with a homogenous phase and fine microstructure because the combustion process can not be controlled after the ignition in SHS process [6]. In addition, it is also difficult to fabricate high purity products with a homogenous phase due to the complexity of manipulation in RRP process [8]. Another novel approach, in-situ fabrication method by laser cladding, has been extensively studied to produce composite materials with better mechanical properties [9], [10], [11]. In-situ fabrication method is easy to realize the approaches of alloying the intermetallics with other elements, controlling the microstructure and enhancing the properties of intermetallic compounds. Moreover, there are few studies that have been performed for in-situ synthesized Ni3Al intermetallic compound coating by laser cladding [9], especially for researching the relationship between the microstructures and mechanical properties.

In the present study, single Ni3Al intermetallic compound phase coating was in-situ synthesized by laser cladding with preplaced Ni and Al mixed powders, and the effects of the laser cladding parameters on the phase composition, microstructure and tribological properties of Ni3Al coating were systematically studied.

Section snippets

Experimental

Powders mixtures of elemental Al powder (30–150 μm, 99.5% purity) and Ni powder (∼75 μm, 99.0% purity) with composition Ni75Al25 (at.%) were used as the starting materials and they were mechanically milled by a common planetary ball mill just for homogeneous mixture before laser cladding. The columnar blocks of 1Cr18Ni9Ti stainless steel with the size of Ф45 mm × 16 mm were used as the substrates. Before laser cladding, the working surface of the stainless steel was ground to a surface roughness of

Preparation of Ni3Al coatings

Fig. 1 shows the SEM micrograph of the Ni75Al25 mixed powders before laser cladding. It can be seen that the Al particles (gray contrast) had an irregular flaky shape and Ni particles (white contrast) were nearly uniform in size with a cauliflower-like shape or an irregular flocculent shape. Fig. 2 presents the XRD patterns of the mixed powders and the laser cladding coatings. As can be seen from Fig. 2a, there are only Ni and Al peaks which indicates that no mechanical alloying of powders

Conclusions

The single Ni3Al phase coating was successfully in-situ synthesized by laser cladding from initial elemental powders under appropriate power density and energy density. The laser cladding Ni3Al coating was continuous, smooth, free from pores and cracks, and with an excellent bonding to the substrate.

The laser power density and energy density had crucial influence on the microstructures and tribological properties of the Ni3Al coating. It is found that the Ni3Al coating synthesized under the

Acknowledgements

The authors wish to acknowledge the Program of “863” (Grant No. 2006AA03A219), and “The program of the light in China's western region (2006)” for financial support.

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