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In this study, a heat source model designed explicitly for rectangular laser heat sources was developed to simulate the temperature field during the laser hot wire cladding process. The influence of the temperature field on the solidified microstructure was investigated. The difference in morphology and size of solidified microstructure was mainly caused by temperature gradient and cooling rate. The grain morphology in the edge region was mainly columnar crystal with small size. The grain morphology in the central area was mainly equiaxed crystals with the larger size. This study provided a reference for understanding the characteristics of the solidification microstructure and its formation during laser hot wire cladding process.

Interfacial thermal resistance in Al-SiC composites was evaluated by comparing the measured thermal conductivity and the calculated thermal conductivity. Al-20vol.%SiC composites changing SiC particle size, 3 μm to 30 μm, was fabricated by spark plasma sintering and heat treatment. Effective thermal conductivity was measured with the steady state thermal conductivity measuring device. Effective thermal conductivity was also calculated by using SEM image and the measured relative density. Comparing the measured thermal conductivity and the calculated thermal conductivity, interfacial thermal resistance in Al-SiC composites was evaluated as about 1.0x10-8 (m2K)/W.

The improvement of thermal conductivity of tool steel is extremely important for order to achieve life prolongation of metal die used in die-casting. In order to improve the thermal conductivity without the degradation of mechanical properties, VGCF (vapor grown carbon fiber) and TiB2 particles added in tool steel (SKD61) and to obtain the composites. Composites was fabricated by spark plasma sintering (SPS). Before sintering, SKD61 powders with 70μm in diameter and 1.9-3.8 vol. % VGCF with 0.15-0.2μm in diameter and 10-20μm in length or 4-8 vol. % TiB2 particles with 2.62μm in average diameter was mixed by V shape type ball milling or planetary ball milling. Composites were sintered at 1273K with 50 MPa. The relative density of all composites is higher than 97%. The thermal conductivity improved from 20W/mK to 36W/mK by adding 8 vol. % TiB2 particles, and to 25W/mK by adding 1.9 vol. % VGCF. On the other hand, the tensile strength of 1.9 vol. % VGCF/ SKD61 composites prepared under the condition of V shape type ball milling has 2200MPa. Composites with addition of 4vol. % TiB2 particles with V shape type ball milling and 1.9 vol. % VGCF with planetary ball milling is almost equal to the monolithic alloy. Good mechanical properties of the composites are caused by the grain refinement or interfacial strengthening by adding dispersants. But as increasing the contents of dispersants, the aggregation of the dispersants degrade the mechanical properties.

The improvement of thermal conductivity of tool steel is a very important problem to achieve life prolongation of a metal die used in press forming and die-casting and obtain large size or complex shape products with good mechanical properties. To improve the thermal conductivity without the degradation of mechanical properties, some kind of dispersants were added into tool steel 40CrMoV5 in ISO standard. 0.5–1.0 vol. % carbon nanofiber, 4–8 vol. % TiB2 particles with 2.62 micrometer in average diameter and 8 vol. % Cu particles was added in tool steel. Dense composites were fabricated by spark plasma sintering by controlling sintering temperature and time. The thermal conductivity was improved by adding all dispersant. Strength of carbon nanofiber / steel composites increased by adding 0.5 vol. % fiber, but decreased by adding 1.0 vol. % because of aggregation of carbon fiber. Some chemical reaction occurred in TiB2 particles/ steel composites, and the elongation improved because of the boron element in the interface. Cu /steel composites keep good strength compared with monolithic tool steel and the thermal conductivity increased dramatically as increasing Cu contents.

Laser hot wire cladding is an efficient and energy-saving additive manufacturing process, which is used in coating, repair, and 3D printing. In this study, 308L stainless steel wire was deposited on the low carbon steel substrate using Laser hot wire cladding technology. The microstructure evolution and microhardness changes in the heat-affected zone of the substrate and the cladding layer near the laser cladding interface were studied in detail by using optical microscopy, electron backscatter diffraction and microhardness tests. The phase transformations and the relationship between microstructure and mechanical properties of the cladding layer were discussed. Owing to the dual effect of temperature gradient and cooling rate, the grain morphology in the central region of the cladding layer is equiaxed, while the edge region is mostly columnar dendritic morphology along the structural direction. There is a dilution zone composed of single austenite near the interface of the cladding layer. In the cladding layer, the ferrite-austenite solidification mode is dominant, and the austenite-ferrite solidification mode is also found in local areas. The carbon migration process from the substrate to the cladding layer promotes the austenite-ferrite mode. The heat-affected zone microstructure consists mainly of ferrite and tempered bainite, and slatted martensite can be observed near the interface. The electron backscatter diffraction results demonstrate the existence of martensite in the heat-affected zone. The texture is more apparent in the cladding layer, while the heat-affected zone contains more residual strain and higher dislocation density. The average grain size in the heat-affected zone region is about 4 μm, while the average grain size in the cladding layer is above 14 μm. The hardness of the heat-affected zone near the interface is the highest due to numerous factors, such as grain size, microstructure transformation and dislocation density. The yield strength increases with the decrease of grain size and texture strength, demonstrating the correlation between microstructure and mechanical properties.

Laser hot wire cladding (LHWC) technology has been proved to be a very efficient laser cladding manufacturing process due to its advantages of fast deposition rate, high material utilization rate, and less environmental pollution. In this study, LHWC technology was used to prepare multiple layers of 308L stainless steel coatings on ordinary mild carbon steel substrates. The microstructure of the weldment section was evaluated by optical microscopy (OM). The results showed that the heat-affected zone (HAZ) of the sample was small, with a height of 1.58 mm and an area of 14.28 mm2. The metallurgical bonding between the substrate and coating was good. Because of the temperature gradient and grain growth rate, the grain morphologies in the different coating regions were different. From the bottom to the top, the grain morphologies were planar crystals, columnar dendrites, and equiaxed grains. Electron backscatter diffraction (EBSD) was used to obtain crystallographic information on the entire section of the sample. The interior of the cladding layer was mainly composed of columnar grains growing along the structural direction, most of which were coarse grains. The matrix and the HAZ consisted of fine equiaxed grains, and the crystal orientations were randomly distributed without obviously preferred orientations. Hardness analysis performed that the hardness of the HAZ was the highest, and the matrix had the lowest hardness. The hardness was higher in the layer-to-layer fusion zone and then gradually decreased with an increase in the cladding height inside each layer. The tensile test results illustrated that the elongation of the cladding layer (44.8 %) was higher than that of the HAZ (32.1 %) and the matrix (20.4 %) because the tensile direction of the tensile sample in the cladding layer was parallel to the laser scanning direction, which improved the tensile performance. The average grain size of the HAZ was the smallest, owing to the effect of fine grain strengthening, and the tensile strength was the highest(585 MPa). According to the tensile fracture profile, the sample matrix, HAZ, and the cladding layer exhibited ductile fractures.

To investigate the influence of the angle of graphite on thermal conductivity and thermal expansion, the thermal properties of graphite reinforce Cu matrix composite was calculated with a simulation code which can take account of the angle of graphite at cross-section face. In this research, the orientation of graphite tends to be distributed parallel for the reason of the hot press during SPS process. Thermal conductivity of Cu matrix composite can be improved with the addition of graphite which has the improved orientation distribution. The result of the simulated thermal conductivity is as same as the measured thermal conductivity. Therefore, the simulation method mentioned in this article could be used for calculating thermal conductivity from cross-section figures of the composite which reinforced by a 2-dimensional material.

Pure aluminum (Al) has been used as high performance heat sink, electrical line and power supply line because of its light-weight, good thermal and electrical conductivities and high cost performance. On the other hand, the higher performance heat sink and eletrtorical line at room and high tempertture are reqired because of the increment of the power density and higher integration of semiconductor and LED. The use of Al matrix composites is one of suilable solution, because these parts needs multi functional propertes. In this study, titanium die-broide (TiB2) particles was selected as the dispersant in Al matrix composites because of its good thermal and electrical conductivity, and good mechanical propertes. At first, the mixed power of Al and TiB2 particles was obtained from six kinds of mixing process, which parameters are conventional boll milling, ultrasonic vibration after conventinal milling, planetary ball milling, which milling process was performed in wet process with ethanol and dry process. 20 vol. % TiB2/ Al composites was obtained from spark plasma sintering. The dence comopsites with over 98% in relative density with highly dispersed TiB2 particles was obtained from wet mixing process. But the tensile strength of the composites prepared from dry mixing process is higher than that of wet mixing process. The thermal conductivity of the composites is about 120 W/mK, and the obvious diferrence between the wet process and dry process was not observed.

Steady state thermal conductivity measuring device was designed to measure the effective thermal conductivity of composites. Computer simulations of thermal conduction revealed that the designed device over estimates the effective thermal conductivity, and the correction coefficient was suggested. With this designed device, the effective thermal conductivities of Al/SiC particle-dispersed composites were measured by changing the size of SiC particles from 0.3 μm to 3 μm. The critical element size which could determine the optimal size of reinforcements have been suggested, and validity of the critical element size for Al/SiC composites was confirmed. The thermal conductivity of the composites including small SiC particles was degraded by the interfacial thermal resistance between the matrix and the reinforcement. On the other hand, the thermal conductivity of the composites including large SiC particles was not affected by the interfacial thermal resistance. These results suggest that consideration of the critical element size is valid.

In order to obtain the high performance materials with high thermal conductivity, high electrical conductivity, low thermal expansion, good mechanical properties and low density, TiB2 particle dispersed aluminum (Al) composites was developed by spark plasma sintering. As these properties are affected by the dispersibility of the particles, the relationship among the dispersibility of dispersant and the thermal conductivity and mechanical properties was investigated, 20 vol. % TiB2 dispersed Al composites with different dispersibility were fabricated by spark plasma sintering (SPS). The dispersibility was estimated quantitatively by using the definition method of local number of particles (LN2DR method), and two composites having 6.884 and 4.839 for number of LN2DR was obtained. Thermal conductivity of the composites with homogeneous distribution of TiB2 particles was lower than that with heterogeneous distribution and clustering. On the other hand, the tensile strength of the composites improved as increasing temperature compared with Al block. Furthermore, strength of the composites with homogeneous distribution of TiB2 particles at 200°C and more was higher than that of the composites with heterogeneous distribution and clustering.

In this study, the coating method suitable for producing high-quality film on aluminum substrate was investigated by using different surface treatment to each specimen before electrodeposition. Microstructure of coating cross section was observed with Electron Prove Micro Analyzer (EPMA). Vickers hardness of coating surface was measured. The measurement of polarization behavior of aluminum in CrO3-H2SO4 electrolyte with ZrO2 addition was carried out to investigate corrosion resistance. The addition of ZrO2 particles increased Vickers hardness of Cr coating. The existence of Zr in the coating was confirmed by point analysis from coating cross section. Polarization point was shifted higher by dispersing ZrO2 particles into the plating bath, and this means that corrosion resistance was improved by the addition of ZrO2 particles.

The relationship between heat treatment and mechanical properties of Al-Si-Mg alloy was investigated. Solution treatment at 808K for 6 hours, preliminary aging at room temperature for 60 hours and artificial aging at 473K for 1 hours were conducted. Not preliminary aged samples were prepared for comparison. The strength improved and the elongation decreased with increasing the amount of Mg. This trend was seen both preliminary aged and not preliminary aged samples. However, preliminary aged samples showed relatively high tensile strength and elongation comparing with not preliminary aged samples. EPMA analysis revealed that the precipitation of Mg2Si in preliminary aged samples was larger than that of not preliminary aged samples, and which possibly contributed to the improvement of strength of the preliminary aged samples. Thermodynamic calculation showed that Mg2Si phase was not undissolved at the solution temperature, 808K, and these undissolved Mg2Si particles might influenced on mechanical properties negatively.