Ruangdaj Tongsri

Effect of Reaction between Fe and Carbide Particles on Mechanical Properties of Fe-Base Composite

Sintered Fe-5 wt. % carbide (SiC or TiC) composites have been prepared via a powder metallurgy (P/M) route. Two carbide particle sizes, < 20 µm and 20-32 µm, were mixed with Fe powder. The powder mixtures were compacted and sintered at 3 different temperatures, 1100, 1150 and 1200 °C. Microstructures of sintered Fe-5 wt. % SiC composites showed evidence of SiC decomposition. The decomposed Si and C atoms diffused into Fe particles resulting in formation of solid solution of Si and C in Fe during sintering. During cooling, the solid solution of C in Fe decomposed to pearlite structure (ferrite and cementite (Fe3C) lamellar structure). Microstructures of sintered Fe-5 wt. % TiC composites showed no evidence of TiC decomposition at the investigated sintering temperatures. Because of the reaction between SiC and Fe, tensile strength and hardness of the sintered Fe-SiC composites were higher than those of the sintered Fe. Experimental results showed that strength and hardness of the sintered Fe-SiC composites increased with increasing sintering temperature and with decreasing SiC particle size. In contrast, mechanical properties of the sintered Fe-TiC composites were inferior to those of the sintered Fe. The reason of poor mechanical properties may be attributed to poor bonding between Fe and TiC particles.

Effects of Cooling Rate and Carbon Content on Mechanical Property of Sintered Fe-Cr-Mo Alloys

Advanced high strength steel (AHSS) was prepared using the conventional ‘press and sinter’ process.The compacts of ultralow carbon Fe-Cr-Mo powder with carbon additions (base metal powder admixed with 0.1,0.2 and 0.3 wt.% graphite) and without carbon addition (plain base powder) were sintered in a vacuum furnace at pressure of 1.28 x 10-5MPa at 1280 °C for 45 min. After sintering, the sintered specimens were continuously cooled with different nitrogen gas pressures of 0, 2500 and 5000 mbars (or 0, 0.25, 0.5 MPa). Mechanical properties of the sintered alloys were strongly controlled by carbon contents and cooling rates after sintering. The sintered specimens, with 0.3 wt.% carbon and cooled by nitrogen of 5000 mbars, showing superior tensile strengths and good ductility, had microstructures dominated by carbide-free bainitic structures and some retained austenite. The sintered specimens with lower carbon contents and cooled under slower cooling rates, having lower tensile strengths but slightly higher ductility, had microstructures with lower bainite volume fractions and even without bainitic structures. The dominant phase in the sintered specimens with low strength but high ductility was ferrite.

Comparative Studies on Wear Behaviour of Sintered 316L Stainless Steels Loaded with h-BN and MoS2

Mechanical properties and wear behavior of stainless steel embedded with different solid lubricants were investigated. Hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2)-embedded 316L stainless steels (SS316L/h-BN and SS316L/MoS2) were prepared by powder metallurgy method. Various h-BN and MoS2 contents (10, 15 and 20 vol%) were mixed with 316L stainless steel powders and then sintered at 1200°C in H2 atmosphere for 60 min. The experimental results showed that small boride phase and h-BN powder occupied the pores in the microstructure of SS316L/h-BN composite whereas the MoS2 second phase occupied the pores of the sintered 316L matrix in the microstructure of SS316L/MoS2 composite. The addition of h-BN decreased the sintered density and hardness whereas that of MoS2 gave the opposite effect. Dry sliding wear behavior of composites was investigated by using pin-on-disc test rig at the sliding speeds of 0.1 and 0.2 m/s and the applied load of 3 N. The results showed that the MoS2 composites had higher wear resistance than the h-BN composite but the h-BN composite yielded a better friction reduction.

Effect of h-BN Content on the Sintering of SS316L/h-BN Composites

In this work, the three compositions of hexagonal boron nitride (10, 15 and 20 vol. %)-embedded 316L stainless steel (SS316L/h-BN) composites were prepared by a conventional powder metallurgy technique and then sintered at varying temperatures of 1100 to 1250°C for 60 min in H2 atmosphere. The h-BN content and sintering temperature were found to affect the microstructure and hardness of the composites. The hardness decreased with increasing h-BN content and was improved by increasing the sintering temperature. Microstructure results revealed that the boride phase was formed at the grain boundary at the sintering temperature higher than 1150°C and the boride phase formation was observed to transform the h-BN in the composites.

Influences of M–Sn intermetallics (M = Ni, Cu) prepared by mechanical alloying on phenol hydroxylation

This work discusses the effect of the crystal structure of Ni–Sn and Cu–Sn intermetallic catalysts on phenol hydroxylation. All catalysts were prepared via the mechanical alloying (MA) technique which is a green process for catalyst preparation. The results showed that the prepared catalysts consisted of monoclinic (Ni3Sn4 and Cu6Sn5) and hexagonal (Ni3Sn and Cu6Sn5(HT)) crystal structures. The catalytic activity of all synthesized catalysts for phenol hydroxylation demonstrated that both Ni3Sn4 and Ni3Sn exhibited better catalytic activity than Cu6Sn5 and Cu6Sn5(HT), and Ni3Sn, having a hexagonal crystal structure, showed the best catalytic activity (>97% conversion) at 363 K, 3 h, 1 : 4 phenol : H2O2, and 50 mg of catalyst content, giving CAT (60.28% yield) and HQ (36.82% yield) with no over-oxidation of CAT and HQ as time elapsed.

Sintered Titanium-Hydroxyapatite Composites as Artificial Bones

The design of engineered bone substitutes takes biocompatibility and mechanical compatibility into account as prerequisite requirements. Titanium (Ti) and hydroxyapatite (HA) with chemical formula of Ca10(PO4)6(OH)2, show good biocompatibility and are known as biomaterials. To combine metal powder (Ti) and ceramic powder (HA) as a composite material with mechanical properties comparable to those of natural bones needs strategy. In this work, powder metallurgy process was employed to produce Ti-HA composites, with nominal HA powder contents in the range of 0-100 vol.%. Mixtures of Ti and HA powders were pressed in a rigid die. Sintering was performed in vacuum atmosphere. The as-sintered specimens were tested on biocompatibility in a human-osteoblast cells. It was found that processing and materials parameters, including compaction pressure, control the composite microstructures and mechanical properties. Laboratory bone tissue culturing showed that a bone tissue could grow on the artificial bones (sintered Ti-HA composites).

Microstructure, Hardness and Wear Properties of Sintered Fe-Mo-Si-C Steels with Spheroidal Graphite Iron/Compacted Graphite Iron-Like

Sintered Fe-Mo-Si-C steels were prepared from pre-alloyed Fe-0.85Mo powder added with fixed 4wt.% silicon carbide powder and varied graphite powder contents. It was found that the graphite powder addition caused morphological change from black nodular to black vermicular particles and resulted in decrease of black nodular/vermicular particle fraction, increase of pearlite fraction and slight change of ferrite fraction. The black nodular particles were either graphite or Fe-Mo-Si-C/graphite core-shell particles whereas vermicular particles were totally composed of carbon. The microstructural features showed influence on mechanical property of the sintered Fe-Mo-Si-C alloys. Wear properties of the sintered steels were strongly affected by their microstructural components. The sintered Fe-0.85Mo+4wt.%SiC steels showed highest friction coefficient and volume loss. Addition of graphite to the sintered Fe-0.85Mo+4wt.%SiC steels, not only changed morphology and chemistry of black particles but also reduced friction coefficient and volume loss. The reduction of both determined wear properties were attributed to the presence of vermicular graphite particles.

Modification of Microstructure and Tensile Property of Sintered Fe-Cr-Mo-C Steel by Nickel Addition

Nickel is one of the alloying elements promoting the formation of acicular ferrite at the expense of proeutectoid ferrite. The Ni addition reduces the steady-state nucleation rates of grain boundary ferrite allotriomorph in Fe-C-Ni alloys. Due to such reasons, Ni was added to modify the microstructure of the sintered steel, investigated in this study, with the aim of improved mechanical properties. The sintered steel, produced from pre-alloyed Fe-Cr-Mo powder mixed with 0.3 wt.% C, was modified by Ni addition and cooling rate. The alloy compositional change was performed additions of varied Ni contents of 1.0, 1.5, 2.0, 2.5 and 3.0 wt.%. The material processing variables were investigated by using two different cooling rates of 0.1 and 5.4 °Cs-1. Under the cooling rate of 0.1 °Cs-1, the sintered Fe-Cr-Mo-3C steel without Ni addition showed dual-phase microstructure consisting of ferrite (soft phase) and bainite (hard structure). With Ni additions, the dual-phase microstructure was replaced by bainitic structure. Microstructural heterogeneity was observed due to the presence of Ni-rich areas, which increased with increasing added Ni contents. Under the cooling rate of 5.4 °Cs-1, the sintered Fe-Cr-Mo-3C steels with and without Ni additions showed bainitic structure. Microstructural heterogeneity was similar to that of slowly cooled steel. Ni additions not only modified the sintered steel microstructure but increased tensile strength and elongation. In general, Ni pushes the C-curve of pearlite transformation to the right hand side and lowers the martensite start temperature. The absence of ferrite from the sintered steel with only 1 wt.% Ni addition and slowly cooled at 0.1 °Cs-1 suggests that Ni strongly suppresses the austenite → ferrite transformation. In another word, Ni promotes bainite formation in the sintered Fe-Cr-Mo-Ni-C steels.

Effect of Aluminum Addition on AlxCoFeMnNiZn Multi-Component Production

Five multi-component alloy (MCA) formulations of CoFeMnNiZn (MCA01), Al0.5CoFeMnNiZn (MCA02), Al1.0CoFeMnNiZn (MCA03), Co5Fe5Mn30Ni20Zn40 (MCA04) and Al8.4Co4.6Fe4.6Mn27Ni18.4Zn37 (MCA05) were prepared by mechanical alloying and melting process (MAM). Five-component alloys of MCA01-MCA05 were designed using empirical formulae for high entropy alloys. Phase formation and microstructure were evaluated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that MCA01 was partially melted by MAM process. However, MCA02-MCA05 could be melted and cast by MAM process. The microstructures of as-cast MCA02 and MCA03 showed dendritic solidification. Nevertheless, the as-cast MCA04 showed microstructure similar to that of Ni-based superalloy, i.e., the as-cast MCA04 consisted of γ matrix and γ′ phase. Moreover, egg type core shell structure was found in the interdendritic regions of the MCA05 alloy. In addition, the Al-added MCA02 and MCA03 alloys showed crystal structures of FCC1, FCC2 and BCC. MCA04 alloy demonstrated crystal structure of FCC whereas MCA05 alloy had crystal structures of FCC and Primitive Cubic.

Fe-Sn Intermetallic Compound Synthesized via Mechanical Alloying and Liquid Phase Sintering

This investigation aimed to synthesize an iron (Fe)-tin (Sn) intermetallic compound (FeSn2) by using a two-step process of mechanical alloying (MA) and liquid phase sintering (LPS). We demonstrated experimentally that this process was able to produce the FeSn2 intermetallic compound. Two different mechanical alloying procedures for producing mechanically alloyed Fe-Sn powders were explored. In the first, mixtures of as-recieved Fe and Sn powders were mechanically alloyed. In the second, the as-received Fe powder was pre-milled first and the as-received Sn powder was then added and mechanically alloyed. Under the same liquid phase sintering conditions, the sintered materials produced via the first mechanical alloying procedure showed that the FeSn2 content increased with increasing sintering time and left small traces of unreacted Fe and Sn materials. In the sintered materials produced via the second mechanical alloying procedure, only the FeSn2 phase was observed for all sintering times. The two-step process using the second mechanical alloying procedure performed better; it synthesized more of the FeSn2 intermetallic compound.