Tungwai Leo Ngai

Mechanical, friction and wear behaviors of a novel high-strength wear-resisting aluminum bronze

By studying microstructural effects on the mechanical and tribological behaviors of aluminum bronzes, a novel high-strength wear-resisting aluminum bronze (KK) has been developed by optimizing microstructures, modifying, adding special elements and controlling the casting process. The mechanical properties, friction and wear behavior of this alloy have been tested and compared with two other commercial aluminum bronzes of the same class. Experimental results show that the properties of the novel KK bronze are much superior to those of the other bronzes.

Effects of Mn content on the tribological behaviors of Zn-27% Al-2% Cu alloy

Friction and wear characteristics of a Zn-27% Al-2% Cu alloy, modified with Ti and misch metal, with different Mn contents, coupled with steel have been studied. A pin-on-disk tribometer was used to measure the friction coefficient of alloy samples under different loads, speeds and lubricating conditions while the wear volume and temperature rise of the lubricant were measured by a cylinder-on-ring wear tester. Friction and wear characteristics of these Mn-containing alloys were compared with those of ZA-27. Effects of Mn content on the tribological behaviors and microstructures were studied and the relationships between the tribological characteristics and the microstructures of the alloy were also analyzed. Experimental results indicate that the addition of Mn can significantly improve the tribological behaviors of the Zn-27% Al-2% Cu alloy. Finally, an optimum Mn content for the best overall mechanical properties and tribological behaviors was obtained.

A study of aluminum bronze adhesion on tools during turning

Abstract M2 high-speed steel (HSS) tool and YW1 cemented carbide tool were used to turn a high strength wear resisting aluminum bronze. Workpiece adhesion was found on both the rake and flank of all samples. Adhesion was more severe and more uneven on the HSS tool than on the cemented carbide tool. Droplet-like particles formed from partial melting of the HSS tool’s surface were found on the open surface of the adhered bronze layer. An optical microscope, scanning electron microscope and electron probe microanalysis were employed to study the adhered materials.

Wetting behaviour of laser textured Ti3SiC2 surface with micro-grooved structures

In the present paper, micro-grooved Ti3SiC2 surfaces with different roughness were fabricated by pulsed laser processing. The surface topography and chemical composition of smooth and micro-grooved surfaces were characterised. The wetting behaviours of smooth and micro-grooved Ti3SiC2 surfaces such as static contact angle, anisotropic wettability and contact angle evolution versus time were investigated. The experimental results show that micro-grooved structures can be efficiently fabricated on Ti3SiC2 surface by laser processing. The contact angle of micro-grooved surface was increased by 64.2° compared with that of smooth surface. The difference values of contact angles between perpendicular and parallel direction were < 10°. The wetting state of droplet on textured surface was close to Cassie–Baxter model.

Effect of Si Content on the Synthesis of Ti3SiC2 Bulk Material by Pressureless Sintering

Ti3SiC2 is a bioinert material. The combination of high fracture toughness, excellent corrosion resistance and easy machinability make it a new class of potential biomaterials for orthopedic applications, dental implants, and fixation devices for the bone. In this paper, effect of Si concentration on the sintering of Ti3SiC2 bulk material was reported. Ti3SiC2 bulks were fabricated by pressureless reactive sintering of powder compacts made of Ti, Si and graphite powders. Nearly pure Ti3SiC2 bulk was obtained by reactive sintering of the powder compact, with a nominal composition of 3:1.1:2 in molar ratio of Ti:Si:C, at 1500 °C for 120 minutes. TiC, a non-preferable impurity was avoided by the appropriate addition of excess Si (relative to stoichiometric composition of 3:1:2 in Ti3SiC2). However, too much Si will result in the formation of significant amount of TiSi2 and SiC in the sintered Ti3SiC2. Microstructure of the prepared Ti3SiC2 bulks was analyzed by scanning electron microscope. Phase constituent analysis was carried out by x-ray diffraction. Effect of Si content on the density of sintered samples was also studied.

A Study on Ti3SiC2 Reinforced Copper Matrix Composite by Warm Compaction Powder Metallurgy

Increasing density is the best way to increase the performance of powder metallurgy materials. Conventional powder metallurgy processing can produce copper green compacts with density less than 8.3g/cm3 (a relative density of 93%). Performances of these conventionally compacted materials are substantially lower than their full density counterparts. Warm compaction, which is a simple and economical forming process to prepare high density powder metallurgy parts or materials, was employed to develop a Ti3SiC2 particulate reinforced copper matrix composite with high strength, high electrical conductivity and good tribological behaviors. Ti3SiC2 particulate reinforced copper matrix composites, with 1.25, 2.5 and 5 mass% Ti3SiC2 were prepared by compacting powder with a pressure of 700 MPa at 145°C, then sintered at 1000°C under cracked ammonia atmosphere for 60 minutes. Their density, electrical conductivity and ultimate tensile strength decrease with the increase in particulate concentration, while hardness increases with the increase in particulate concentration. A small addition of Ti3SiC2 particulate can increase the hardness of the composite without losing much of electrical conductivity. The composite containing 1.25 mass% Ti3SiC2 has an ultimate tensile strength of 158 MPa, a hardness of HB 58, and an electrical resistivity of 3.91 x 10-8 Ω.m.

Studies on Preparation of Ti3SiC2 Particulate Reinforced Cu Matrix Composite by Warm Compaction and Its Tribological Behavior

Conventional powder metallurgy processing can produce copper green compacts with density less than 8.3 g/cm3 (a relative density of 93%). Performances of these conventionally compacted materials are substantially lower than their full density counterparts. Warm compaction, which is a simple and economical forming process to prepare high density powder metallurgy parts or materials, was employed to develop a Ti3SiC2 particulate reinforced copper matrix composite with high density, high electrical conductivity and high strength. In order to clarify the warm compaction behaviors of copper powder and to optimize the warm compaction parameters, effects of lubricant concentration and compaction pressure on the green density of the copper compacts were studied. Copper compact with a green density of 8.57 g/cm3 can be obtained by compacting Cu powder with a pressure of 700 MPa at 145°C. After sintered at 1000°C under cracked ammonia atmosphere for 60 minutes, density of the sintered compact reached 8.83 g/cm3 (a relative density of 98.6%). Based on these fabrication parameters a Ti3SiC2 particulate reinforced copper matrix composite was prepared. Its density, electrical conductivity, ultimate tensile strength, elongation percentage and tribological behaviors were studied.

Warm Compaction Forming of a Binder-Treated Fe-Base Material

Abstract It is well known that increasing density is the best way to increase the performance of powder metallurgy (PM) parts. Conventional PM processing can produce iron-base parts with density less than 7.2 g/cm3. Their mechanical properties are substantially less than their full density counterpart. With minor modification on the conventional PM equipment, green compact density of 7.4 g/cm3 can be obtained by warm compaction. Binder-treated technique is an efficient and cost-effective process that can produce high green strength compacts with consistent alloy content and reduce dusting. The mixed powder is bonded by organic binder, which is burned out during sintering. In this study, high density and high green strength iron-base compacts were obtained by warm compacting binder-treated iron-base powder at 150°C using a pressure of 700 MPa. Sintered compact with density of 7.38 g/cm3, tensile strength of 624 MPa and elongation of 4.8% can be obtained after sintering at 1120°C for 1 h under a cracked ammonia atmosphere. Effects of warm compaction parameters, such as binder concentration and compaction temperature, on the properties of the sintered material were investigated. Green and sintered compact densities, spring back effect and mechanical property were measured and analyzed. Present paper demonstrated that binder-treated warm compaction process can not only reduce the powder segregation and increase the green compact strength, but also reduce the use of additives such as lubricant and binder.

Interfacial Stability of a Spark Plasma Sintered Mo-Ti3SiC2 Layered Composite

Mo-Ti3SiC2 layered composite was successfully prepared by spark plasma sintering at 1573 K for 20 min under a pressure of 50 MPa in vacuum. The Mo and Ti3SiC2 layers were metallurgically bound together without noticeable superficial defects and micro-cracks at the interface. The fabricated Mo-Ti3SiC2 layered composite was annealed at 1273 K under vacuum for 5, 10, 20 and 40 h to study the composite’s thermal stability. Three intermediate layers, Mo2C, MoSi2 and Ti5Si3Cx, were formed at the interface. Experimental results showed that the Mo-Ti3SiC2 layered composite prepared in this study has good interfacial stability at elevated temperature.

Compaction Experiment on the Newly Designed Warm High Velocity Compaction Equipment

In order to develop high density powder metallurgy forming technology, a new concept combining high velocity compaction and warm compaction called warm high velocity compaction (WHVC) was presented. A new warm high velocity compaction forming equipment which adopts gravitational potential energy instead of hydraulic cylinder as hammer driver was designed. By means of the newly developed equipment, a preliminary study on warm high velocity compaction was performed. 316L stainless powder compacts with green density of 7.47 g/cm3 were obtained; the density is much higher than those prepared by conventional high velocity compaction. These results demonstrate that the newly designed equipment can basically meet the demand of warm high velocity compaction and the new forming method is superior to the conventional high velocity compaction. In addition, Densification mechanism of WHVC was also discussed.