APPLICATIONS OF X-RAY STRESS MEASUREMENT FOR INTERFACE AREA OF Ni 3 Al SYSTEM INTERMETALLIC COMPOUND COATING

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1 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume APPLICATIONS OF X-RAY STRESS MEASUREMENT FOR INTERFACE AREA OF Ni 3 Al SYSTEM INTERMETALLIC COMPOUND COATING *Takayuki MUROTANI **Tomonori YANO ***Hajime HIROSE and **** Akira IKENAGA *Department of Mechanical Engineering, Dalian University, Dalian Economic & Technical Development Zone Dalian, , P.R. China **Graduate School of Kanazawa University, Kakumamachi Kanawzawa Ishikawa , Japan *** Kinjo University Research Center, Kasamamachi 1200, Matto Ishikawa , Japan **** Graduate school of Engineering Osaka Prefecture University, 1-1 Gakuencho Sakai Osaka , Japan ABSTRACT The Ni 3 Al intermetallic compound coating technique was used to coat for ordinary metal samples. In this experiment, the Ni 3 Al intermetallic compound was coated on a spherical carbon cast-iron substrate and austenite stainless steel substrate using the low-temperature + thermal diffusion method. X-ray stress measurement and FEM analysis were carried out in the coating layer surface. Based on our results, the following conclusions are made: experimental measured residual stresses in the Ni 3 Al coating layer are smaller than the calculated value from the FEM; concentration of residual stress is found at the interface between substrate and the coating layer. INTRODUCTION The intermetallic compound Ni 3 Al is of great interest because of its high melting point, oxidation, and corrosion-resistance. However, it is difficult to make Ni 3 Al coating using ordinary techniques [1]. The recent application of composite material is excellent because the coating material has low cost and high temperature durability. The low-temp hot press + thermal diffusion process method is a technique that uses the thermal diffusions between the elements that compose the intermetallic compound [2]. In this method, the powder mixture is heated and it generates the diffusions of the powder by keeping the temperature comparatively lower than other methods [2]. The authors evaluated the preparation conditions and joining quality in Ni 3 Al coating layers on various substrates, and of particular interest is the residual stress due to the different mechanical properties of the coating, the substrate, and its effect on the interface joining quality. It is known that residual stresses were generated by the difference in the coefficient of thermal expansion (CTE) of coating layer and substrate during preparation. In addition, residual stresses are caused by

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3 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume Table 1. Chemical composition of substrate. (wt.%) SUS304 (Austenite stainless steel) C Si Mn Ni Cr BC6 (Bronze cast) Cu Sn Pb Zn FCD370 (Spheroidal graphite cast iron) C Si Mn P S Mg Cr Cu Ceramic die Load(30MPa) Vacuum pomp Vacuum chamber Powder compact (Coating layer) Substrate Electric furnace Figure 1. Schematic illustrations of hot press apparatus. the misfit of mechanical properties. These stresses strongly influence material strength. Residual stress in coating layer affected the bending and bonding strengths [3]. We used an X-ray method such as the sin 2 ψ technique to measure residual stress acting on Ni 3 Al coating layer. The influence of substrates on the residual stress in coating layer was examined. These experimental results were compared with the simulated thermal stress results from the finite element method (FEM). Our investigation used three kinds of substrates: spheroidal graphite ductile cast iron, bronze cast metal, and austenite stainless steel. SPECIMEN We produced the coating layer by using the low-temp hot press + thermal diffusion 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 5µm) and Al powder (purity 99.9wt%, mean grain size 3µm). The powder mixture was compacted to diameter=10mm, and thickness=1.0mm at 400MPa by using the metal die. The chemical compositions and mechanical properties of the substrate austenite stainless steel (Japanese Industrial Standard: JIS-SUS304) and spheroidal graphite ductile cast iron (JIS-FCD370) and bronze cast (JIS-BC6) are shown in Tables 1 and 2. The specimen was fixed between the ceramic die of the hot press device, as shown in Figure 1. The vacuum in the furnace was Pa. While pressing mechanically with 30MPa from the vertical direction of the interface, the inside temperature of the furnace was brought to 873K. The low-temperature hot press (first heating process) held the furnace with constant temperature of 873K, 0.9ksec. And the furnace was cooled to room temperature. Once again heating the furnace made it 1133K. The diffusion process (second heating process) held the furnace with constant temperature of 1133K, 3.6ksec. The samples were not pressured during the second heating process. Finally, the furnace was cooled to room temperature.

4 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume Table 2. Mechanical properties of material components in this study. Young's modulus (GPa) Poisson's ratio Coefficient of thermal expansion (x10-6 K -1 ) Specimen FCD370 SUS304 BC6 Ni 3 Al Z Incident X-ray Z' Table 3. X-ray stress measurement conditions. Characteristic X-ray Cr-Kα Diffraction plane (hkl) Ni 3 Al:220 Fixed time (sec) 20 Tube voltage (kv) 30 Tube current (ma) 10 Diffraction angle (deg) 152 Number of ψ Irradiated area (mm 2 ) Measurement optics (13) 4 6 Side-inclination method Y Y ψ 2 θ scan Detector Coating layer X Substrate σ Figure 2. The optic system for X-ray stress measurement. DISTRIBUTION OF RESIDUAL STRESS The residual stress distribution was measured using the RIGAKU MSF-2M X-ray stress measurement device with the sin 2 ψ technique [4].The measurement conditions are shown in Table 3. The optic system was Substrate Coating layer Figure 3. FEM model for thermal analysis. set up in the stress radial direction for σ X (1/4 axial symmetric model) as shown in Figure 2. The measurement area was a central part of the Ni 3 Al coating layer of the surface. To enable the residual stress distribution measurement in the vertical direction from the surface to joining interface direction, the surface layer was removed one by one by the electrolysis grinding technique using 5% sulfuric acid and 95% methanol. Since the X-ray penetration depth in the Ni 3 Al coating layer is smaller than that in common industrial materials, consequently, the X-ray determined residual stresses is expected to represent the mean value only in the X-ray penetration depth. These things are supported by the fact that the thickness of the coating layer is 1mm, which is very large compared with the X-ray penetration depth. X

5 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume Residual stress σ x,mpa FCD370 based BC6 based SUS304 based Distance from interface, µm Residual stress σ x,mpa FCD370 based BC6 based SUS304 based Distance from interface,µm Figure 4. Relation between Residual stress and distance from interface (X-ray). Figure 5. Relation between Residual stress and distance from interface (FEM). Thus, we can regard that measurement result reflects only residual stress in the Ni 3 Al coating layer. Thermal stress for coating prepared at high temperature was calculated using the direct joint model with ANSYS 5.7 finite element method (FEM) software. Model of the FEM analysis is shown in Figure 3. EXPERIMENTAL RESULTS AND DISCUSSION: RESIDUAL STRESS DISTRIBUTION IN Ni 3 Al COATING Figure 4 shows the relationship between measured residual stress and the distance from interface. Compressive residual stress is small in the case of the FCD370 substrate specimen. This observation can be explained by the fact that the elastic constants and the CTE of Ni 3 Al and FCD370 are very close. It is thus believed that the material is better when its component properties are equal. Thus the joining quality of FCD370 specimen is not strongly affected by the heating process. Compressive residual stress in Ni 3 Al with SUS304 substrate is the largest of all substrates. We believe this is caused by the large CTE difference in the component materials. The compressive residual stress is increasing near the interface area. The difference of the CTE is large in specimens BC6. Therefore, residual stress of material is large. It is thus possible to evaluate the joining quality by measuring residual stress. It is suggested that the residual stress was presented mainly in the region near the interface between the coating and the substrate. The stress distribution of FEM-simulation of the coating layer is shown in Figure 5. As seen in Figure 5, compressive residual stress is obtained in all the specimens of coating layer. Residual stress is the largest near the interface of Ni 3 Al and SUS304, which has the largest CTE difference combination. Position of the stress concentration in near interface area differs from measurement residual stress. The clarification of these factors is a future subject. However, behaviors of the residual stress except in that section are agreeing well.

6 Copyright JCPDS - International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume CONCLUSIONS In this experiment, the Ni 3 Al intermetallic compound was coated on a spherical carbon cast-iron substrate and austenite stainless steel substrate by using the low-temperature + thermal diffusion method. X-ray stress measurement and FEM analysis were carried out in the coating layer surface. Based on our results, the following conclusions are made: 1. Residual stresses in the coating layer were measured by X-ray diffraction method. Compressive residual stress was obtained in Ni 3 Al coating layer, which increases as the difference between CTE of coating and substrate increases. 2. Experimental measured residual stresses in the Ni3Al coating layer are smaller than the calculated value from the FEM. Concentration of residual stress is found at the interface between substrate and the coating layer. REFERENCES [1] Ikenaga,A.; Goto,Y.; Nitta,Y.; Kawamoto,M.; Kobayashi,K.; Uenishi,K., JFS, 1996, 68, [2] Murotani,T.; Taguchi,T.; Ikenaga,A.; Hirose,Y., JFS,2002,74, [3] Toyoda,M., Interface Mechanics, Rikogakusha; Japan, 1991, [4] The society of Materials Science, Japan, X-Ray Stress Measurement, Yo-kendo; Japan,1981,