H.M. Wang

Microstructure and wear resistance of laser clad Ti5Si3/NiTi2 intermetallic composite coating on titanium alloy

Abstract A wear resistant Ti 5 Si 3 /NiTi 2 intermetallic composite coating was fabricated on substrate of a titanium alloy BT9 by laser cladding with (wt.%) Ni–30Ti–10Si elemental powder blends. The laser clad intermetallic composite coating has a rapidly solidified fine microstructure consisting of Ti 5 Si 3 primary particles uniformly distributed in the NiTi 2 matrix and is metallurgically bonded to the titanium substrate. The laser clad Ti 5 Si 3 /NiTi 2 intermetallic composite coating has high hardness and excellent wear resistance under dry sliding wear test conditions. The excellent wear resistance of the laser clad Ti 5 Si 3 /NiTi 2 intermetallic composite coating is attributed to the coatings high hardness, strong intermetallic atomic bonding and refined microstructure.

'In-situ' weld-alloying/laser beam welding of SiCp/6061Al MMC

Abstract In this paper, ‘in-situ’ weld-alloying/laser beam welding with titanium as alloying element is utilized to join SiCp/6061Al MMC in order to prevent the formation of the needle-like harmful Al4C3 phases in the weld. Microstructure of the weld is characterized as functions of alloying content and processing parameters. Results show that the needle-like harmful aluminum carbides are completely eliminated. A central fusion weld joint reinforced by TiC, Ti5Si3 and Al3Ti is produced by ‘in-situ’ weld-alloying/laser beam welding of SiCp/6061Al MMC, while some large pores are formed in the partly melted zone.

Microstructure and wear resistance of a laser clad reinforced Cr3Si metal silicide composite coating

Abstract A rapidly solidified wear resistant Cr 3 Si reinforced metal silicide composite coating was fabricated on a 0.20% C low carbon steel by laser cladding, using Crue5f8Siue5f8Ni elemental powder blends. The microstructure of the coating was characterized by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The wear resistance of the coating was evaluated under dry sliding wear and pin-on-disc abrasive wear test conditions. The microstructure of the coating consists of rapidly solidified Cr 3 Si primary dendrites and interdendritic NiCrSi complex silicide solid solution. Due to the rapidly solidified microstructural characteristics and the presence of a large amount of hard Cr 3 Si phase, the laser clad Cr 3 Si metal silicide composite coating has excellent wear resistance under both dry sliding wear and pin-on-disc abrasive wear test conditions.

Annealing laser-melted ductile iron by pulsed Nd:YAG laser radiation

Abstract Laser-melted ductile iron was rapidly annealed by pulsed Nd:YAG laser beam irradiation. The cementite-graphite phase transformation occurred rapidly during the short duration pulsed laser beam scanning. As a result, novel iron-base alloys containing either ultra-fine nodular graphite particles or both rapidly solidified cementile and ultra-fine graphite particles have been fabricated. The unusually accelerated cementite-graphite phase transformation and the production of the ultra-fine novel microstructure were predominantly due to the micro-annealing effect of the cyclic temperature fluctuations induced by the pulsed laser beam radiation.

Phase transition and mechanical properties of Ni30Cu20Mn37＋xGa13-x（x=0–4.5） alloys

Ni30Cu20Mn37+xGa13−x (xxa0=xa00–4.5) alloys were studied with the phase transformation and mechanical properties. With the increase of Mn content, the martensitic transformation temperatures increase and the Curie temperature decreases. Simultaneously, the room temperature microstructure evolves from single phase of austenite to dual phases containing martensite and precipitation. Both the ductility and the strength of the polycrystalline alloys are significantly improved by the precipitation. Coupled magnetostructural transition from weak magnetic martensite to ferromagnetic austenite is obtained in both single-phase and ductile dual-phase alloys.

Microstructure and Mechanical Properties of Plasma Arc Welding Joint for Laser Melting-Deposited AerMet100 Ultrahigh-Strength Steel

The repair of laser melting-deposited AerMet100 ultrahigh strength steel (UHSS) heat-treated samples with groove machined was conducted by low-cost plasma arc welding (PAW). And the microstructure and mechanical properties of welding joint were examined by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-hardness test and the tensile mechanical test. The experimental results indicated that the welding zone with low hardness values mainly consisted of columnar grains with about 200μm width which epitaxial growth from substrate grains, and in which the cellular morphology character appearing at the bottom in comparison with dendrite with lateral branching appearing at the top. Three zones, i.e., sufficient quenched zone, insufficient quenched zone and high-temperature tempered zone, were divided by heating affected temperature and microstructure characteristic in heat affected zone (HAZ), and there was a lowest hardness value region distributed in high-temperature tempered zone. Compared to that of undamaged heat treated forged one, the tensile mechanical property of the repaired laser melting deposited sample got a few decrease but was still well, in which the tensile strength σb, yield strength σs, elongation δ5 and reduction of area Ψ was 1627Mpa, 1285Mpa, 10.5% and 45% respectively. In addition, the isothermal thermal simulation test surveyed that the tensile fracture position locating in high-temperature tempered zone with the lowest hardness value could ascribe to the growth of alloy carbide and increase of reverted austenite in over-aged temperature.

Thermal fatigue crack growth behaviours of laser deposited Ti60A near α titanium alloy

Abstract Thermal fatigue damage of high temperature titanium alloys and thermal fatigue crack growth (TFCG) behaviours are of great concern for severe temperature fluctuating environments. Cyclic thermal fatigue tests of heating to 700°C for 55 s followed by water cooling for 3 s at 20°C per cycle were performed with laser deposited Ti60A (Ti–5·54Al–3·38Sn–3·34Zr–0·37Mo–0·46Si) alloy. Thermal fatigue crack growth paths including crack length and crack growth directions were examined, as were their correlations with microstructure changes during the thermal fatigue process. Results show that local coarsened lamellar α developed by the interaction between cyclic thermal stress and oxygen atom interstitial solution effect occurs in the alloy after 800 cycles. Thermal fatigue cracks initiate after 800 cycles. Subsequently, total crack length increases with the volume fraction of local coarsened lamellar α from 800 to 2000 cycles. The enhanced oxygen penetration process plays a key role in the TFCG process.