Shielded metal arc butt welded joints for 9%Ni steel using nickel-based filler metal were analyzed by optical microscopy, scanning electron microscope, as well as transmission electron microscopy. The nanoindentation method was used to study the correlation between the structure and micromechanical properties of the fusion welded joint. The results show that there is a microstructural evolution from melted deposit to 9%Ni base steel. A significant coarse lath martensite-bainite mixture has been obtained in 9%Ni steel close to the fusion boundary while the retained austenite distributing in grain boundary of lath martensite has reduced to an undetectable level. In fusion boundary, an intermetallic layer has been observed which corresponds to the epitaxial growth of weld metal. The analysis of stress-strain behavior using nanoindentation shows that the heat-affected zone of coarse grains exhibits ductility loss and quantitative plastic deformation failure. The fusion boundary has the lowest value of yield stress while the coarse grained heat affected zone has the maximum value of yield stress.

An analytical model is developed to predict residual stresses formed during plasma cladding process. This is based on the force and moment balances and misfit strain caused by differential coefficient of thermal expansion (CTE) of substrate and cladding layers during cooling. The model can be implemented by a simple programming. Residual stresses can be predicted from a knowledge of material properties, temperature of substrate and layers and specimen dimensions. Residual stresses are calculated after each layer rather than as a whole. Specific results can be obtained for the distribution of residual stresses within Co-based layers system. The effect of temperature of substrate and layers, the number of layers, the curvature of a composite beam on the residual stresses are discussed. It has been found that the residual stresses decrease with the increase of preheating temperature of substrate and inter-layer temperature of layers. The curvature increase with increasing layer number.

Influence of solid solution temperature on microstructures and corrosion properties of CoNiCrMo alloy were investigated by means of optical microscopy (OM), scanning electron microscope (SEM) and electronic differential system. The corrosion resistance of CoNiCrMo alloy in 0.9%NaCl aqueous solution was also investigated. The results indicated that with the increase of solution treatment temperature, the dendrites of CoNiCrMo alloy gradually disappeared. Thus, the corrosion resistance of the alloy decreased. When the solution temperature is 1200°C, the dendrites almost disappeared and most carbide dissolved, and begins to spheroidization. The corrosion resistance of CoNiCrMo alloy treated at 1000°C for 1h is the highest than the one at 1100 °C and 1200°C. Its self-corrosion potential is-424mV and self-corrosion current density is 1.02×10-8 A/cm 2 .

Nanoindentation test, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were introduced to investigate the mechanical properties and microstructure of microscopic regions of the nickel-based welded joint. Five indentation series were performed across the weld zone including base metal (BM), coarse grained heat affected zone (CGHAZ), partially melted zone (PMZ), weld metal near the partially melted zone and weld metal center (WM). The mechanical properties (E, H, and n) were then estimated from the load on sample-displacement into surface curves (P-h) data of nanoindentation and SEM analysis results. The results showed that the average nano-hardness value (H) was obviously increased in the CGHAZ. WM has the highest values of elastic modulus (E). BM has the highest plastic rheology stress exponent (n). At the same time, the relationship between the plastic rheology depth and the plastic rheology was also discussed.