Effect of SiC particle size and content on strain-based pore closure rate studies on Al–SiC P/M composites during cold upsetting

A series of laboratory-scale powder metallurgical upsetting experiments was conducted during cold upsetting on sintered Al–SiC composites. Aluminium–silicon carbide composites containing 5%, 10%, 15% and 20% SiC of four different particle sizes, namely 50, 65, 120 and 180 μm, were completely investigated. The pore closing rate and the formability strain index value were evaluated and discussed in terms of matrix and geometric work hardenings. Three novel strain-based pore closure rate indices were proposed and analysed for all the above said preforms, and their variations with respect to their relative density were plotted and discussed.     

A real time marking inspection scheme for semiconductor industries

The deformation and densification behaviour of sintered hypo-eutectoid steel ring preforms with carbon contents of 0.35% and 0.65%, under cold axial deformations, have been studied in order to understand the influence of various forming parameters such as flow stress and percentage axial height reduction on the densification process. Four different conditions of material deformations, namely, pure upsetting, deformation constrained along radial inward direction, deformation constrained along radially outward direction and, finally, deformation of material and pores constrained along both inward and outward radial directions have been applied during the axial cold forming tests. Results of the investigations have established that highest densification rate is achieved in rings subjected to the most severe flow constraint of fully restrained radial flow, at comparatively lower levels of axial deformations. Both carbon content and initial sintered ring geometry are also found to influence the deformation as well as densification rates during the cold forming process. Ring preforms of lower initial geometry, namely, 6:3:2 exhibit better densification rates irrespective of the mode of flow, but require lesser flow stress values, compared to those of initial geometry of 6:3:4. The densification process is observed to follow an almost linear trend in the case of fully constrained axial deformation, whereas, under less severe flow constraints, the same is observed to follow second or third order polynomials.     

Effect of sintering temperature and time intervals on workability behaviour of Al–SiC matrix P/M composite

The investigation on the effect of sintering temperature and time intervals on workability behaviour of Al–SiC powder metallurgy composites during cold upsetting was attempted in the present work. Three levels of sintering temperature and time have been considered to evaluate their effect on workability behaviour. The amount of SiC reinforcement content has been varied as 0%, 10% and 20%. The experimental results were analyzed for workability under triaxial stress state condition as a function of the relative density. The Formability Stress Index (β_σ), the Formability Strain Index (β_ε), stress ratio parameters namely σ_θ/σ_eff and σ_z/σ_m were obtained for all the cases. As a result, the exhibited tremendous variations in the various parameters for different sintering temperatures and time intervals were studied and reported.     

Experimental investigations on the microstructure and mechanical properties of sinter-forged Cu and Mo-alloyed low alloy steels

The present investigation pertains to the study of the mechanical properties and fracture behavior of sinter-forged low alloy steels containing copper (Cu) and molybdenum (Mo) as alloying elements. Elemental powders of atomized iron, graphite, molybdenum, and copper were mixed in suitable proportions using a ball mill, compacted in a 1,000 kN hydraulic press using suitable cylindrical die–punch combination and sintered at 1,000 ± 10°C in a muffle furnace for a period of 120 min in order to yield the alloy compositions (by weight) such as Fe–0.5% C, Fe–0.5% C–1% Cu, Fe–0.5% C–2% Cu, Fe–0.5% C–1% Mo, and Fe–0.5% C–2% Mo. The sintered cylindrical preforms were then subjected to hot upset forging to near theoretical density and subsequently machined off to standard size in order to carry out the mechanical tests such as hardness, tensile, and impact tests. Addition of Cu and Mo to the plain carbon steel has been observed to enhance the tensile strength as well as hardness of the sinter-forged alloys. The presence of Mo carbides in the microstructure of the alloys further reinforces this observation. The impact strength of this alloy has been observed to be reduced considerably due to the addition of the alloying elements.     

Fabricating hollow turbine blades using short carbon fiber-reinforced SiC composite

The development of hollow turbine blades fabricated by nickel-base superalloy is limited by its high density and low operating temperature (<1,100 °C). A new technology for fabricating hollow turbine blades of fiber-reinforced SiC composite was put forward. The chemical corrosion process of DSM Somos 19120 resin mold was investigated, and the pyrolysis of phenolic resin and the infiltration of liquid silicon were analyzed by using scanning electron microscope and X-ray diffraction. The influence of carbon fiber content on fracture strength and fracture toughness of fiber-reinforced SiC composite was investigated using the measurement of three-point flexural strength test. Results showed that stereolithography molds of photosensitive resin were corroded perfectly using KOH alcohol water solution. The porous carbon preforms were obtained after phenolic resin was pyrolyzed from 400 to 800 °C, which were then infiltrated with molten silicon to gain SiC matrix at the temperature of 1,450 °C in 1 h. The fracture strength and fracture toughness of SiC ceramic matrix were enhanced with the increase of short carbon fiber content. The maximum fracture strength and fracture toughness of samples were about 270 MPa and 5.1 MPa m^1/2, respectively. Finally, hollow turbine blades were successfully fabricated using short carbon fiber-reinforced SiC composite.     

颗粒尺寸及组合对SLS碳化硅预制体精度的影响

采用热法包覆方法制备了不同颗粒组合的碳化硅陶瓷粉末,并利用选区激光烧结(SLS)工艺制备了碳化硅陶瓷预制体,研究了颗粒尺寸及组合对激光烧结陶瓷预制体成形精度的影响规律。结果表明：颗粒尺寸及组合对激光烧结陶瓷预制体成形精度的影响显著,预制体翘曲量随颗粒尺寸的增大而减小,表面粗糙度和尺寸误差均随颗粒尺寸的增大而增大;相对于单一颗粒,由双尺寸颗粒组合制备的预制体的翘曲量减小了11%~50%,表面粗糙度Ra值减小了12%~20%,尺寸误差减小了38%~79.6%。     

Forging simulation of sintered powder compacts under various frictional conditions

This research is to investigate the deformation characteristics of sintered compacts and the evolution of voids in the forging process under different frictional conditions. The Gurson–Tvergaard yield criterion was used to describe the plastic behaviour of porous materials, while the material parameters were empirically determined.Experiments and finite element analysis were conducted to examine the processes. The material properties of sintered preforms were ascertained from both the uni-axial tension and compression tests. The finite element models were verified with the upsetting experiments under different frictional conditions. A simulation of forging the gear blank under various contact situations was performed as well. Studies show that voids lead to the degradation of the strength of the sintered materials. Friction at contact interfaces contributes to the non-uniformity of deformation and the density variation in the workpiece after large deformation.     

Workability studies on Al–5%SiC powder metallurgy composite during cold upsetting

The present technical work reports on the workability performance along with the consolidation behavior of aluminum (Al) and Al–5% silicon carbide (SiC) powder metallurgy composites during cold compaction. An experimental work has been carried out to investigate the powder compaction behavior of Al–SiC metal matrix composites. SiC of particle sizes 120, 75, and 45 μm has been pre-alloyed with Al powders of particle size ranging from ?37 to 75 μm. Various particle size additives of SiC have been used as a second-phase particle in this work with the intension of predicting the mechanical and metallurgical properties of the metal matrix composites studied. The pressure applied for the preparation of compacts have been considered as 220–260 kN in order to prepare the samples of heights in the range of 30 to 32 mm, and the diameter of the compacted sample was 26.11 mm. The densification during compaction is measured by means of the presence of voids in the compacts applying the mass constancy principle. The effect of particle size on the metal matrix composites proposed has been completely investigated under two different stress state conditions such as plane and triaxial.     

Effect of Sintering Temperature and Atmosphere on Nonlubricated Sliding Wear of Nano-Yttria-Dispersed and Yttria-Free Duplex and Ferritic Stainless Steel Fabricated by Powder Metallurgy

The nonlubricated sliding wear behavior of nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel against a diamond tip was studied. The stainless steel samples were fabricated by a conventional powder metallurgy route in which nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel powders were cold compacted and then conventionally sintered at either 1000, 1200, or 1400°C in an argon atmosphere. For comparison, another set of samples was sintered at 1000°C in a nitrogen atmosphere. The wear behavior of sintered stainless steel samples against a diamond indenter was investigated using a pin-on-disc apparatus at 10 and 20 N loads and at a constant speed of 0.0041 m/s. It is proposed that yttria-dispersed stainless steels showed higher wear resistance compared to yttria-free stainless steel due to their improved hardness and density. Stainless steel sintered in a nitrogen atmosphere exhibited better wear resistance than those sintered in an argon atmosphere due to the formation of hard and brittle Cr₂N. The wear mechanisms of stainless steels against diamond were found to be mainly abrasive and oxidative. Semiquantitative analysis of the worn surfaces and wear debris confirmed the occurrence of oxidation processes during wear.     

Near net shape processing of a sintered alumina component: adjustment of pressing parameters through finite element simulation

Near net shape forming of alumina powder by cold die pressing and pressureless sintering was investigated. From experimental data of triaxial compression test of alumina powder, a hyperbolic cap model with a critical state line was proposed for densification of alumina powder at room temperature. For pressureless sintering, the phenomenological model for densification and viscous behavior of alumina powder proposed by Kim and co-workers was used. The constitutive models were implemented into a finite element program (ABAQUS) to simulate densification of alumina powder under cold die pressing and pressureless sintering. Finite element results were compared with experimental data for density distribution and deformation of an alumina powder compact under cold die pressing and pressureless sintering. New conditions of compaction were then proposed to reduce the distortion of the sintered part.     

Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.     

Effect of fabrication parameters on the pore concentration of the aluminum metal foam, manufactured by powder metallurgy process

In this paper, the effect of fabrication parameters on the pore concentration of aluminum metal foam manufactured by powder metallurgy process is studied. Aluminum metal foam specimens were fabricated from the mixture of aluminum powders (mean particle size 60 μm) and NaCl at 10,20,30,40(wt) % content under 200, 250, 300, MPa Pressures. All specimens were then sintered at 630°C for 2.5 hours in an argon atmosphere. For pore formation (foaming), sintered specimens were immersed into 70°C hot running water. Finally the pore concentration of specimens was recorded to analyze the effect of fabrication parameters (namely NaCl ratio, NaCl particle size and compacting pressure) on the foaming behavior of compacted specimens. As a result of the study, it has been recorded that the above mentioned fabrication parameters are effective on pore concentration profile while pore diameters remained unchanged.     

Interface Structure and Wear Behavior of Cr26 Ferrous Matrix Surface Composites Reinforced with CTCP

Using cast tungsten carbide particles (CTC_P) and reduced iron powders as raw materials, the porous ceramic preforms with honeycomb, strip, and layer structure, respectively, were prepared by loose sintering process; then, the CTC_P/Cr26 ferrous matrix composites were fabricated by casting infiltration process. The microstructure of the composites was analyzed by SEM, XRD, and EDS. The results show that a sintered shell forms as a result of the reaction of Fe and W₂C in the CTC_P during loose sintering process; the inner part of the shell around the CTC_p consists of WC and Fe₃W₃C phases, while the outer part between the particles is dominated by Fe₃W₃C. Therefore, the strength of preforms is enhanced because the particles are connected with each other by sintered shell. During casting infiltration process, a transition layer constituted by WC and Fe₃W₃C formed at the interface of CTC_p and the matrix due to the dissolution and precipitation of the sintered shell in the high-temperature liquid iron. The three-body abrasive wear behavior of the composites was investigated. The result shows the wear resistance of honeycomb structure composite is comparable to that of whole layer (WL) structure composite, which is three times of heat-treated Cr26. However, the honeycomb structure composite has higher performance/cost ratio owing to the lower CTC_p volume fraction and higher strength and toughness compared with the WL structure composite.     

Application of ANN in the prediction of the pore concentration of aluminum metal foams manufactured by powder metallurgy methods

In this work, the effect of fabrication parameters on the pore concentration of aluminum metal foam, manufactured by the powder metallurgy process, has been studied. The artificial neural network (ANN) technique has been used to predict pore concentration as a function of some key fabrication parameters. Aluminum metal foam specimens were fabricated from a mixture of aluminum powders (mean particle size 60 μm) and NaCl at 10, 20, 30, 40(wt)% content under a pressure of 200, 250, and 300 MPa. All specimens were then sintered at 630°C for 2.5 h in argon atmosphere. For pore formation (foaming), sintered specimens were immersed into 70°C hot running water. Finally, the pore concentration of specimens was recorded to analyze the effect of fabrication parameters (namely, NaCl ratio, NaCl particle size, and compacting pressure) on the foaming behavior of compacted specimens. It has been recorded that the above-mentioned fabrication parameters are effective on pore concentration profile while pore diameters remain unchanged. In the ANN training module, NaCl content (wt)%, NaCl particle size (μm), and compacting pressure (MPA) were employed as inputs, while pore concentration % (volume) of compacts related to fabrication parameters was employed as output. The ANN program was successfully used to predict the pore concentration % (volume) of compacts related to fabrication parameters.     

Rolling/sliding contact fatigue life prediction of sintered and hardened steels

Among the several competing mass production methods, powder metallurgy (PM) techniques give much contribution as a means of saving material and energy. It also delivers the material with good fatigue properties that are good substitute for the conventional materials. Application of PM parts is getting wider in many areas such as automotive parts, agricultural equipment, business machine, electrical and electronics, hardware and industrial applications, etc. Many structural machine components made of PM route like gears and bearings experiences rolling–sliding contact fatigue conditions (RSCF). Contact fatigue is a type of failure commonly found in the surface of bearings, gears etc., and this type of failures decide the useful life of these structural parts. Presence of friction between the bodies normally encountered in service, many influence the contact fatigue behavior. The use of new materials and in particular sintered materials requires a thorough understanding of contact fatigue behavior for better product design and development. RSCF on sintered and hardened of 7 gm/cc density (FLC 4608-110HT, Fe–Ni PM steel) were carried out in a specially designed test rig for different contact parameters such as contact stress and slide to roll ratio. Twin-disc type rolling/sliding experimental set-up has been developed in laboratory to simulate the sliding and rolling between two rollers. Contact stress distribution and RSCF life prediction models suitable for sintered and hardened steel were also developed. The predicted life was compared with the experimental RSCF life for sintered and hardened steel.     

孔挤压强化和工艺参数研究

孔挤压强化可以显著提高机械连接的疲劳强度。采用有限元方法建立了孔挤压强化轴对称模型,得到了孔壁残余应力分布状态,建立了孔壁残余应力和孔径、板件厚度、挤压强化过盈量等工艺参数之间的关系曲线。结果表明,周向残余应力和孔径、挤压强化过盈量之间为对数关系,和板件厚度之间为线性关系;径向残余应力和孔径、挤压强化过盈量之间为对数关系,和板厚(以2.5mm为分界线)之间为线性关系,为孔挤压强化效果的定量化认识奠定了基础。     

激光织构和碳基薄膜复合处理提高钛合金摩擦学性能研究

在重载滑动干摩擦条件下，对比不同织构密度的钛合金表面的摩擦学性能；在耐磨性最好的织构密度钛合金表面再制备碳基薄膜，并与直接在钛合金表面制备的碳基薄膜的摩擦学性能进行对比。结果表明：3种低织构密度条件下，TC4钛合金的摩擦因数减小、磨损率降低；随着织构密度的增大，钛合金材料的摩擦因数变化极小，磨损率有所增加；在织构密度5.95%的钛合金表面制备的碳基薄膜，因织构微凹处产生的小微湍流，减少了摩擦阻力，使得其摩擦因数相比直接在钛合金表面制备的碳基薄膜的摩擦因数有所减小。织构化碳基薄膜的磨损率比钛合金的磨损率降低了99.31%，比直接在钛合金表面制备碳基薄膜的磨损率也降低了约60%，这是因为高接触应力摩擦过程中触发石墨化转变，被磨损的石墨化颗粒碎片嵌入织构微凹中，抑制了摩擦接触界面的磨损行为。     

Small-hole arrays of ceramic material manufactured by micro powder injection molding

Ceramic substrate with three kinds of small-hole arrays (the minimum diameter is 400?μm) was manufactured by micro powder injection molding. The homogeneity, thermal, and rheological properties of the feedstock was characterized by means of SEM, Archimedes method, TGA, DSC, and capillary rheometer, respectively. The feedstock has good uniformity and the viscosity of feedstock accords with the pseudo-plastic behavior which is suitable for micro powder injection molding. The test results also show that the linear shrinkage of small holes is lower than the substrate which is important to mold design and size contraction of the sample. Moreover, the porosity of the sintered substrate is lower than that of the thin wall between two neighborhood small holes. Good surface roughness of the sintered samples is obtained by using sub-micron ZrO₂ powder which is even lower than molded surface. The relative density and hardness of the ceramic substrate with small-hole arrays sintered under 1,500°C for 2?h is 98.3% and 13.68?GPa, respectively.     

Sliding wear behavior of mesocarbon microbeads based carbon materials

The sliding wear behavior of mesocarbon microbeads (MCMBs) based carbon materials was investigated. Samples were sintered at 1300 °C from pure MCMBs without ball-milling (C0) and ball-milled MCMBs doped with 3, 5, 10 wt.% nano-SiC (C3, C5 and C10). The results indicated that C0 sample had poor sliding wear property; ball-milling and doping nano-SiC contributed to the improvement of sliding wear property. The mean friction coefficient values of the C0–C10 samples against H62 brass alloy were 0.38, 0.24, 0.21, and 0.30, respectively. Mass loss increased with increasing sliding time, and C0 and C3 had the highest and lowest mass loss, respectively. The worn surface images showed C0 sample had broad wear tracks and was free from debris layer, while the worn surfaces of C3 and C5 were rather smooth because of the formation of adherent contact films without any significant fracture. These good sliding wear properties were related to small grains, uniform high hardness and large amount of aromatic layers along contact surface.     

高频电液激振冷挤压数值模拟及其减载实验研究

针对冷挤压成形过程中流动应力大、零件成形所需压力高的问题,提出了一种新的挤压工艺,设计了一种新的电液高频轴向振动激励冷挤压试验平台及相应冷挤压模具。利用Deform-3D软件建立了有限元分析模型,分析了在轴向振动激励下该模型的成形过程降载效果,精确地模拟了万向节轴套的冷挤压成形过程的挤压力的变化,比较了传统挤压形式下和轴向振动激励形式下的成形压力值,通过挤压试验验证了模型模拟的准确性。试验结果表明,该新的挤压成形工艺能使万向节杯套成形压力降低21.78%,减载效果明显。研究结果表明,这种新的成形工艺可以为一些难成形零件的冷挤压成形加工打下良好基础。