Jinjiang He

Microstructure characteristics of ZrC-reinforced composite coating produced by laser cladding☆

Abstract In the present work, metal-matrix composites layers reinforced by various sizes ZrC0.7 particles were formed by laser single and overlapping cladding on a medium carbon steel, which are in situ synthesized by laser melting of precursor mixtures of Fe-based alloy powders and Zirconium powder using a 3 kW continuous wave CO2 laser. A high quality coating free of cracks and porosities was obtained. Excellent bonding between the coating and the medium carbon steel substrate was ensured by the strong metallurgical bonding. The chemical compositions, surface morphology, microstructure, interface structure and the distribution of the ZrC0.7 particles of the clad layers were analyzed by Optical microscopy, field emission scanning electron microscopy with associated energy dispersive X-ray spectroscopy, X-ray diffractometry, and metallography computer analysis system. The microstructure consists typically of dendrites/cells, interdendritic eutectic and dispersed ZrC0.7 particles. The in situ ZrC0.7 particles are distributed within dendrite and interdendritic regions owing to the trapping effect of the advancing solid–liquid interfaces. The average volume fractions of in situ ZrC0.7 particles are less than 1.96% for the single clad layer, and vary from 2.2 to 3.84% for the overlapping layers respectively. The martensite (M) transformation went with the rapid cooling processes also. The microhardness profile across the cross-section of the single clad layer varies from HV0.21000 to 1200. The microstructure of the interface between the clad layer and the substrate is martensite, which shows that there is good metallurgical bonding. The sizes and amounts of ZrC0.7 particles in overlapping layers are larger and more than that of laser single clad layer.

Deposition of PTFE thin films by ion beam sputtering and a study of the ion bombardment effect

Abstract Ion beam sputtering technique was employed to prepare thin films of Polytetrafluroethylene (PTFE). Simultaneous ion beam bombardment during film growth was also conducted in order to study the bombardment effects. Infrared absorption (IR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis was used to evaluate the materials integrity. It was found that PTFE thin films could be grown at room temperature by direct sputtering of a PTFE target. The films composition and structure were shown to be dependent on the sputtering energy. Films deposited by single sputtering at higher energy (∼1500 eV) were structurally quite similar to the original PTFE material. Simultaneous ion beam bombarding during film growth caused defluorination and structural changes. Mechanism for sputtering deposition of such a polymeric material is also discussed.

Plastic properties of nano-scale ceramic–metal multilayers

Abstract Nanoscale TiC–metal (Al, Cu, Fe, W) multilayers were prepared by ion beam sputtering deposition with an intent to study the plastic properties of the ceramic–metal combinations. The multilayers were designed to have different layer thickness arrangements, including component fraction, modulation wavelength, etc. Their toughness and hardness were systematically investigated as well as the laminated structures. It was found that for most TiC–metal multilayers the toughness was significantly improved in comparison with monolithic TiC, but the hardness showed great dependence on the material system. In TiC–Fe and TiC–W systems, the multilayer hardness exhibited a peak value which was even higher than the hardness of TiC. In TiC–Al and TiC–Cu systems, no superhardness effect was detected.

Simulation of nacre with TiC/Teflon multilayers and a study of their properties

Abstract Ion beam sputter deposition was employed to prepare nanoscale multilayers of TiC and a polymeric material, Teflon. The multilayers were synthesized to simulate nacre not only on laminated structures but also on individual layer thicknesses. The laminated architecture was studied as well as the structures of individual layers. Multilayer toughness and hardness were systematically investigated. It was found that the toughness of TiC/Teflon multilayers was significantly improved in comparison with monolithic TiC. But the multilayer hardness experienced a serious decrease. The individual layer thickness arrangement had an influence on both the multilayer hardness and the toughness.

Experimental observations on the mechanical properties of nanoscale ceramic/Teflon multilayers

Abstract Inspired by the ingenious architecture of nacre and its outstanding mechanical properties, we prepared nanoscale ceramic (TiC, Si3N4, B4C) /Teflon multilayers by ion beam sputtering deposition at room temperature. The toughness, hardness and tribological properties were systematically investigated as well as the multilayer structures. It was found that the toughness of ceramic/Teflon multilayers were all significantly improved in comparison with the corresponding monolithic ceramic material, but the hardness was decreased. However, there were optimized layer thickness arrangements with which the multilayer toughness and hardness can be favorably combined to obtain better comprehensive properties. It was found by this study that ceramic/polymer multilayers with the optimized layer thickness arrangement had good performance in wear resistance.

Study on nanostructural morphology of Si3N4/TiN multilayer synthesized by ion beam assisted deposition

Abstract The structure and morphology of Si 3 N 4 /TiN multilayer synthesized by ion beam assisted deposition (IBAD) were studied by X-ray diffraction (XRD), Auger electron spectrum (AES) and Field-emmision scanning electron microscopy (FESEM). It was found that a well-defined multilayer structure was formed. The multilayer was composed of polycrystalline TiN and amorphous Si 3 N 4 . The compositions were determined as N:Ti=1 and N:Si=0.9, respectively. Ion beam etching technique was employed to prepare special specimen for FESEM morphology observation. Cross-sectional FESEM was also conducted. Results showed that the Si 3 N 4 layers consisted of granular particles of about 100 nm in size and the particles in TiN layers were much smaller.

Laser producing particulate reinforced Fe-based MMC coatings and industrial applications

This paper presents the research achievements on Fe-based metal matrix composite coatings (MMC) on steel and iron substrates by laser alloying and laser cladding and their industrial applications. The high carbon-equivalent design ensures the good formability and high hardness while eliminates hot cracking during rapid solidification. The jointly adding of strong-carbide-formation-elements promotes the precipitation of large quantity of hard particles. The typical microstructure of the MMC coating characterizes about 4000∼5000/mm2 carbide particles (1∼3 micron in diameter) homogeneously precipitated on iron-base matrix. The average hardness of the coating reaches up to Hv0.2 950∼1050. Tribological test proved that this particulate reinforced Fe-based MMC coating posses excellent wear resistance and couple ability with various different frictional counterparts as well as remarkable decrease of the friction coefficient. Its grain-abrasion resistance is better than that of the plasma sprayed Mo coating and its adhesive-abrasion resistance better than the chromium coating. This MMC coating also demonstrated unique corrosion resistance and contact-fatigue resistance. This particulate reinforced MMC coatings have been successfully applied in rock arms, cam shafts, piston rings of engine, plunger pistons and kerf of cutting knives.This paper presents the research achievements on Fe-based metal matrix composite coatings (MMC) on steel and iron substrates by laser alloying and laser cladding and their industrial applications. The high carbon-equivalent design ensures the good formability and high hardness while eliminates hot cracking during rapid solidification. The jointly adding of strong-carbide-formation-elements promotes the precipitation of large quantity of hard particles. The typical microstructure of the MMC coating characterizes about 4000∼5000/mm2 carbide particles (1∼3 micron in diameter) homogeneously precipitated on iron-base matrix. The average hardness of the coating reaches up to Hv0.2 950∼1050. Tribological test proved that this particulate reinforced Fe-based MMC coating posses excellent wear resistance and couple ability with various different frictional counterparts as well as remarkable decrease of the friction coefficient. Its grain-abrasion resistance is better than that of the plasma sprayed Mo coating and i...

Mechanical performance of laser deposition repairing of in 738 on directionally solidified superalloy blade

Laser deposition is a promising and cost-effective repair and rejuvenation processes for Directional solidified (DS) superalloy blades. This paper focuses on the investigation on mechanical performance of the as-deposited directionally solidified IN 738 structure.Continuous DS columnar structure is available in multi-layer overlap deposition via laser deposition parameter optimization. Heat treatment has no obvious influence on the directional solidification characteristic. Large amount of γ′ particles with size of 100 to 200nm precipitate during heat treatment. Heat treatment decreases the average hardness of the deposition layers from HV0.2397 to HV0.2361. The yield strengths of the deposition layers at room temperature show isotropy in different directions. The ductility is better along directional solidification direction. After heat treatment, the yield strength of the deposition layers decreases about 110MPa. Compared with the DS substrate, the yield strength of the deposition layers is lower but ductility is better. The tensile strength of the deposition layers at 900°C is about 670MPa, similar to the DS substrate. It will decrease about 130Mpa after heat treatment and it is isotropy in different directions. All the fractures in the deposition layers consist of ductile nests which are initiated by carbideThe results indicate the mechanical performance of the deposition layers by laser can meet the need of practical use.Laser deposition is a promising and cost-effective repair and rejuvenation processes for Directional solidified (DS) superalloy blades. This paper focuses on the investigation on mechanical performance of the as-deposited directionally solidified IN 738 structure.Continuous DS columnar structure is available in multi-layer overlap deposition via laser deposition parameter optimization. Heat treatment has no obvious influence on the directional solidification characteristic. Large amount of γ′ particles with size of 100 to 200nm precipitate during heat treatment. Heat treatment decreases the average hardness of the deposition layers from HV0.2397 to HV0.2361. The yield strengths of the deposition layers at room temperature show isotropy in different directions. The ductility is better along directional solidification direction. After heat treatment, the yield strength of the deposition layers decreases about 110MPa. Compared with the DS substrate, the yield strength of the deposition layers is lower but du...

Microstructures and mechanical properties of laminated structural Nb-Ti-Al composites fabricated by laser deposition

Based on design to match the strength and toughness, a laminated structural material made of brittle A15-Nb3Al alloy and ductile B2 NbTiAl alloy using laser deposition was developed. The A15/B2 laminated composites were prepared with different layer thickness ratios. The element compositions and microstructures show periodic variation in the laminated deposition layers and gradual change at the interface within two neighboring layers. Cracks in the brittle A15-Nb3Al alloy layers were effectively limited.The β/B2 phase alloys have much low microhardnesses than that of δ-Nb3Al based alloys. The microhardness distribution of the laminated composites shows periodic variation in the deposited layers and gradual change at the interface within two neighbouring layers.The compressive properties at 900°C and room temperature and the fracture toughness of the laminated composites with different layer thicknesses were studied. The results approve that the laminated composites have both high strength and good fracture toughness.Based on design to match the strength and toughness, a laminated structural material made of brittle A15-Nb3Al alloy and ductile B2 NbTiAl alloy using laser deposition was developed. The A15/B2 laminated composites were prepared with different layer thickness ratios. The element compositions and microstructures show periodic variation in the laminated deposition layers and gradual change at the interface within two neighboring layers. Cracks in the brittle A15-Nb3Al alloy layers were effectively limited.The β/B2 phase alloys have much low microhardnesses than that of δ-Nb3Al based alloys. The microhardness distribution of the laminated composites shows periodic variation in the deposited layers and gradual change at the interface within two neighbouring layers.The compressive properties at 900°C and room temperature and the fracture toughness of the laminated composites with different layer thicknesses were studied. The results approve that the laminated composites have both high strength and good fractur...

Synthesis of Nb3Al high temperature intermetallic compound by laser deposition

Refractory intermetallic compound Nb3Al is expected as a candidate for structural materials operated at much higher temperatures compared to conventional Ni superalloys. This paper presents research work on laser deposition of a powder blend of Nb, Ti, Al pure elements to form Nb3Al intermetallic compound. The research focuses on an alloy composition of Nb-12Ti-22Al (at.%). The fine δ-Nb3Al/β-Nbss intermetallic compound with a composition close to the atom ratios of the elemental powder blend was obtained by laser deposition in an argon atmosphere chamber. The microstructure characterization and phase identification were analyzed by XRD, SEM and TEM. The fine δ/β compound has an average microhardness up to HV0.21022. Although Nb3Al has a negative formation enthalpy, high laser energy density is needed for Nb3Al formation by peritectic reaction. There is a critical crack-free height in laser deposition of Nb3Al under appropriate processing parameters. Beyond the height, the sample cracks due to residual tensile stress induced during laser deposition.Refractory intermetallic compound Nb3Al is expected as a candidate for structural materials operated at much higher temperatures compared to conventional Ni superalloys. This paper presents research work on laser deposition of a powder blend of Nb, Ti, Al pure elements to form Nb3Al intermetallic compound. The research focuses on an alloy composition of Nb-12Ti-22Al (at.%). The fine δ-Nb3Al/β-Nbss intermetallic compound with a composition close to the atom ratios of the elemental powder blend was obtained by laser deposition in an argon atmosphere chamber. The microstructure characterization and phase identification were analyzed by XRD, SEM and TEM. The fine δ/β compound has an average microhardness up to HV0.21022. Although Nb3Al has a negative formation enthalpy, high laser energy density is needed for Nb3Al formation by peritectic reaction. There is a critical crack-free height in laser deposition of Nb3Al under appropriate processing parameters. Beyond the height, the sample cracks due to residual te...