Papers by Keyword: Diffusion Layer

Abstract: The interplay of various hardening and softening processes during explosive welding and post-processing annealing have been analysed in titanium/copper bimetallic sheets using scanning electron microscopy and microhardness measurements. Severe plastic deformation and intermetallics’ formation are typical processes leading to hardening, whereas dynamic/static recrystallization and the transformation of amorphous phases into crystalline ones lead to softening. In the as-welded state the interfacial layers of both parent sheets are severely deformed. However, they can undergo intense recrystalization in areas near large melted zones. Inside the melted zones a wide variety of chemical compositions can be detected, however, most of the phases do not appear in the Ti-Cu equilibrium phase diagram. The post-processing annealing at 973 K for 1 h leads to full recrystallization of severely deformed layers of parent sheets and transforms the non-equilibrium phases forming melted zone into the equilibrium TiCu₄ and Ti₃Cu₄ ones via spinodal decomposition. Simultaneously, the growth of four intermetallic layers: Ti₂Cu, TiCu, Ti₃Cu₄, TiCu₄ situated along the whole interface was detected.

Abstract: In the present scientific work a thickness calculation procedure of an aluminum gas-thermal coating, sprayed on the low-alloyed steel surfaces, in order to provide its effective protection at high temperatures, has been developed. The method is based on the calculations of the diffusion layer thickness with consideration the temperature change on the blank`s surface and on the dependence of the parameter (directly proportional to the diffusion coefficient) on the temperature over the range 700 to 1200 °C.

Abstract: AA4045/AA3003 cladding billets with different clad ratios were fabricated by direct chill casting process. The macrostructures, microstructures, compositions distribution and the mechanical properties near the bonding interface were investigated in detail. The results show that the cladding billet with few defects could be obtained by semi-continuous casting process. The metallurgical bonding was formed due to the diffusions of elements. The decreasing of clad ratio changed the microstructure at the interface and reduced the thickness of diffusion layer. The hardness around the interface is higher than that of AA3003 side but lower than that of the other side, indicating that the interface yield strength is also higher than that of AA3003. After extrusion process, the characteristics of the interface remain that of as-cast cladding billet.

Abstract: Die soldering occurs when molten aluminum sticks to the surface of a die material and remains there after the ejection of the part. This resulted in low productivity and economic value in the foundry industry. Nitriding surface treatment is considered as an effective way in enhancing the service life of AISI H13 steel dies and to prevent soldering effect. The focus of this paper is to investigate the influence of three different surface conditions in terms of roughness, gas nitriding and pretreatment prior to gas nitriding on the soldering effect. Three kind of samples made of AISI H13 steel were pretreated (quenched and tempered) and followed by : shot peened, gas nitrided and shot peening followed by gas nitriding, were immersed in liquid melted ADC 12 Aluminium alloy at 30 seconds, 30 minutes, 2 hours and 5 hours, at a constant temperature of 680^oC in a holding furnace. Characterizations on the surface of the steel were focused on the optical microstructure, microhardness profile, FE SEM observation and enegy dispersive spectrometry mapping. It was found that shot peening prior to nitriding gives a higher surface hardness and depth of nitride layer of H13 tool steel, 1140 HV (>70 HRC) and 120.5 μm, than the nitriding only process, 1033 HV (68 HRC) and 105 μm. The higher the hardness and depth of nitride layer expected would reduce the die soldering effect at the surface of the H13 tool steel dies. It was also found that the only shot peening treatment resulted in a tendency of soldering accompanied by the formation of intermetallic layers ; while soldering is not found on the nitrided and shot peened-nitrided samples.

Abstract: In metal forming process by die casting method, nitriding plays an important role in increasing the surface hardness. The influence of shot peening and shot blasting to the modified. H13 tool steel before nitriding process has been studied. Nitriding has been done in a gas vacuum furnace, at temperature of 510°C for 5 hours. Shot peening was conducted by using steel balls with a pressure of 461 kPa. Shot blasting has been done after shot peening using SiC particles. Characterization of the sample surface before and after the variation process is focused on changing the microstructure, micro hardness distribution, depth and composition nitriding layer. It has been found that shot peening prior to nitriding increase the maximum surface hardness to 1196 HV and effective depth of diffusion layer to 72 μm. Meanwhile, the nitriding without any prior surface treatment produces a maximum hardness of HV 1101.4 with effective depth of diffusion layer of 54 μm. Shot peening prior to nitriding produces white layer thickness of 4.1 μm thicker compared to white layer developed in nitriding without shot peening which produces 3.7 μm. While on nitrided material without any preceded surface treatment did not reveal any white surface layer.

Abstract: This paper has developed one way to produce flexible carbon cloth from artificial cotton cloth carbonized at 1000°C with using (NH₄)₂HPO₄ as impregnation agent and phenolic resin as modification agent. The effects of (NH₄)₂HPO₄ and phenolic resin on bulk resistivity, tensile strength, density, thickness and microstructure of the resultant carbon cloth were investigated. The results show that (NH₄)₂HPO₄ impregnation is helpful to increase the carbon yield of artificial cotton cloth and decrease the bulk resistivity. The fibers in the carbon cloth are bond by carbonized phenolic resin, leading to higher tensile strength and lower bulk resistivity. When mass content of (NH₄)₂HPO₄ was 5% and phenolic resin 54%, flexible and porous carbon cloth was prepared with thickness of 0.27mm, density of 0.34g/cm³, bulk resistivity of 0.06Ω·cm and tensile strength of 2.33MPa, which is promising materials for diffusion layer in fuel cell.

Abstract: The Cu-Ce infiltration layer was formed on 304 Stainless Steel surface by double glow plasma surface metallurgy technology. The effects of heat insulation temperature and heat insulation time on surface alloying concentration, surface hardness and infiltration layer depth were analyzed by comparative test. The results showed: In the experimental range, the contents of Cu and Ce, surface hardness, diffusion layer depth increase with the temperature and time increasing; the deposition layer depth increases with time increasing and decreases with temperature increasing in a certain range.

Abstract: Cutting temperature is the main factor to be considered in the select of coated cutting tools, so the study on the temperature of coated cutting tools is of practical significance. Diffusion layer of coated cutting tools has important implications on cutting heat generation and temperature distribution. In this paper, thickness of diffusion layer is determined by making use of spectrum analysis method to observe elements diffusion between coating and substrate of coated cutting tools. By dividing the diffusion layer into two parts on both sides of interface of coating and substrate, diffusion layer model is established. By integrated use of calculation method of Maxwll-Eucken model, Series model and equivalent thermal conductivity of multi-layer materials, thermal conductivity calculation formula of diffusion layer is derived. Method of thermal conductivity calculation when combining coating and diffusion layer into a whole layer is also put forward. Results of this paper have wide significance for experiment and simulation study on coated cutting tool temperature.

Abstract: The Cu-Ce infiltration layer was formed on 304 Stainless Steel surface by double glow plasma surface metallurgy technology. The effects of source voltage and cathode voltage on surface alloying concentration, surface hardness and infiltration layer depth were analyzed by comparative test. The results showed: In the experimental range, the contents of Cu and Ce, surface hardness, deposition layer depth increase with the source voltage increasing, which is contrary to the cathode voltage; the diffusion layer depth increases with either voltage increasing in a certain range.

Abstract: In this research, 4045/3004/4045 composite ingots were obtained by a semi-continuous casting process. The macrostructure, microstructure, elements distribution, mechanical properties of 4045/3004/4045 triple layers composite were studied. The results show that the composite interface is planar and clean with little evidence of porosity can be achieved by an optimum semi-continuous casting technology. The thickness of diffusion layer near composite interface can be controlled less than 30 μm. The bonding strength can reach to 100MPa which belongs to a kind of metallurgical bonding.