X-ray Stress Measurement for Ni-Al System Intermetallic Compound Prepared by SHS- method

An X-ray diffraction technique was used to measure the residual stress in the surface of a specimen containing a coating of a NijAl intermetallic compound produced bythe SHS (Self-propagation High temperature Synthesis) method. The Ni3Al was using the coating material for spherical carbon cast iron substrate and austenite stainless steel substrate. Differences between the coefftcient of thermal expansion of the coating and substrate were c onlirmed to be the source of compression stress in the coating. INTRODUCTION The recent application of composite material that is low in cost and has an excellent coating material with heatproof, wear-resistant corrosion, and surface modifications is increasing. However, the self-propagation high-temperature synthesis (SHS) methodl’] is a technique that uses the chemical reactions between the elements that compose the intermetallic compound. In this method the powder mixture is heated and is able to generate the combustion reaction of the powder elements by keeping the heating temperature under the melting point of the given compound. ‘2,31 In this study, our purpose is to coat the intermetallic compound on spherical carbon cast-iron and on austenite stainless steel substrate by using the SHS method and to investigate the stress condition inside the coating layer. The thermal stress. inside the material where heat and bond exist is considered to influence the material strength of the coating layer. After where producing the foundation material, the residual stress distribution inside the N&Al coating layer was measured for each specimen. SPECIMEN We produced the coating layer by using the combustion synthesis reaction of the powder compact. The powder was composed of elements in the atomic ratio Ni-25at%Al from Ni powder (purity 99.9wt%, mean grain size 5 ,LL m) and Al powder (purity 99.9wt%, mean grain size 3 p m). The mixed powder was compacted to diameter=lOmm, and thickness= 0.187mm at 400MPa by using the metal dice. The chemical compositions of the substrate austenite stainless steel (Japanese Industrial Standard: JIS-SUS304) and spherical graphite cast iron (JIS-FCD700) are shown Table 1. The micrograph of the cross section of the powder compact is shown in Figure 1. Since the part that is forming lo-20 iu. m spherical clusters in this micrograph, surrounds Ni, is Al, and we are able to confirm that it Copyright (c)JCPDS-International Centre for Diffraction Data 2002, Advances in X-ray Analysis, Volume 45. 275