Zhi Yu Xiao

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.

A Study on Warm Compacting Behaviors of 316L Stainless Steel Powder

The application of warm compaction in stainless steel powders has not been formally reported by now. In this paper, the warm compacting behavior of 316L stainless steel powders had been studied. Results showed that warm compaction was effective in improving the green density and strength of 316L stainless steel powders. Under the compacting pressure of 800 MPa, warm compacted density was 0.20 g/cm3 higher than cold compacted one, and green strength was 52% higher. The optimum warm compacting temperature was 110±10°C. With die wall lubricated warm compaction, the internal lubricant content can be reduced by 0.5 wt%.

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.

Crystallization Kinetics Analysis and SPS Consolidation of Mechanical Alloyed Fe79Ti16P5 Amorphous Powders

Amorphous Fe79Ti16P5 alloy powders were synthesized from commercially available elemental powders by mechanical alloying. The microstructure, thermal stability and crystallization kinetic of as-milled powders were analyzed by XRD, SEM and DSC. Moreover, bulk ultrafine-grained materials were fabricated through spark plasma sintering of the amorphous powders. Results show that the amorphous powders exists two exothermal peaks during crystallization process. The effective activation energies for crystallization are obtained 109.14 kJ/mol and 205.97 kJ/mol for Ep1 and Ep2, respectively, by using the Kissinger method. The mechanical properties of the bulk materials are remarkably improved with the increase in the sintering temperatures. The ultimate compressive strength increases from 1282 MPa to 2015 MPa, but absence of ductility.

Study on Bending Ultrasonic Fatigue Behavior of Sinter-Hardened Fe-2Cu-2Ni-1Mo-1C Materials Prepared by Warm Compaction

Bending fatigue behavior of a sinter-hardened high density (7.4 g/cm3) Fe-2Cu-2Ni-1Mo-1C material fabricated by die-wall lubricated warm compaction of partially-diffuse alloyed powder was studied by bending ultrasonic fatigue testing. Results showed that fatigue strength decreases continuously with the increasing number of cycles. The fatigue failure yet occurs in the regime of exceeding 107 cycles and exhibits no traditional horizontal plateau between 106 and 107 cycles. Fatigue strength was 194 MPa, 239 MPa and 293 MPa at 108, 107 and 106 cycles respectively. Scanning electron microscopy revealed that cracks initiated from large pores on the surface and from pore clusters near the sub-surface. The fatigue cracks initiated both at single and multiple sites. Crack propagation was mainly in a trans-crystalline rupture mode. Fatigue striation and cleavage plane were observed in the crack propagation region and dimples were observed in the fracture zones.

Preparation of Ti3SiC2 Particulate Reinforced Cu 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 8.3 g/cm 3 (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 Ti 3 SiC 2 particulate reinforced copper matrix composite with high density, high electrical conductivity and high strength. Copper matrix composites reinforced with 5, 10 and 15 mass.% Ti 3 SiC 2 particulate 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, ultimate tensile strength and elongation percentage decrease with the increase in particulate concentration, while hardness increases with the increase in particulate concentration. A small addition of Ti 3 SiC 2 particulate can increase the hardness and the wear-resistivity of the composite without losing much of electrical conductivity. Using warm compaction technique, sintered composite with 5 % Ti 3 SiC 2 , has an ultimate tensile strength of 201 MPa with an elongation of 8.1 %, a hardness of HB 68 and a resistivity of 11.04 x 10 -8 Ω m.

Manufacturing of a NbC Particulate Reinforced P/M Iron-Base Valve-Guide Cup

The introduction of ceramic particulate into metallic powder will unavoidably lower the compressibility and formability of the mixed powder. In order to overcome these problems, in this study, warm compaction was introduced in the forming of an NbC particulate reinforced iron-base valve-guide cup, which is used in a combustion engine. Warm compaction was used not only because it can provide compacts with high green density but also it can increase the formability of the mixed powder. The part composed of an iron-base material which possesses 10wt%NbC with a relative density of 97.7%, a tensile strength of 815MPa, an elongation of 1.5%, a hardness of HRC33 and an impact toughness of 11J/cm2. Its working surface composed of an iron-base material which possesses 15wt% NbC with a high relative density of 98.2%, a tensile strength of 515MPa, a hardness of HRC 58 and a remarkable tribological behavior. The sintered part successfully passed a 500 hours bench test. No serious wear on the working surface can be observed after the test. Results indicated that the sintered part has excellent wear resistivity and the NbC particulate reinforced iron-base composite is a suitable material for parts that work under severe wear condition.

Effects of the Delivery Tube Diameter on the Qualities of Cu-9.7Sn-0.2P Alloy Powder Produced by Gas Atomization

Gas atomization is one of the most cost-effective methods for preparing spherical powders. The Cu-9.7Sn-0.2P alloy powder for 3D printing was prepared by a self-developed double nozzle gas atomization technique with different deliver tube diameters, and the particle size and shape of the powder were characterized. Results show that the powder particles are mostly nearly spherical, mixed with a few irregular powders. The average O. Bluntness of the powders are 60~70%, the average Outgrowths are lower than 18%. The deliver tube diameter affects the powder characteristics directly. The increase of the diameter increases the particle size of the powder and reduces the sphericity. At the same time, the adhesion of the satellite powder decreases, the flowability becomes better and the oxygen content drop. The surface and internal structure of the powder are mainly cellular and dendritic structures.

Warm Flow Compaction to Form Cross-Shaped Parts with Threaded Holes

The flowability of W-Ni-Fe powders was evaluated through measuring the lateral pressures at different lateral distances in warm flow compacting. Green densities at different lateral distances were also tested. In addition, cross-shaped parts with threaded holes were trial produced. The results showed that, at lateral distance of 2 mm, the lateral pressure was 101.9 MPa and the green density was 9.09 g·cm-3 when compacted under 600 MPa at 96°C. Warm flow compaction could form cross-shaped parts with lengthwise and lateral threaded holes.

Design and Simulation Based on Virtual Prototype of New Apparatus for High Velocity Compaction

High velocity compaction (HVC) is one of the latest technologies of powder metallurgy (PM), while the prices threshold of Hydropulsor’s HVC presser limited massive application of this technique in vast minor PM enterprises in Mainland China. In the light of this, the paper delivers a new design of HVC apparatus which adopts mechanical springs groups instead of hydraulic cylinder as hammer driver. The virtual prototype and simulation of new HVC apparatus is brought about. The result of simulation shows that new design can basically meet the demand of HVC.