Effect of solution treatment under load on microstructure and fabrication of porous NiTi shape memory alloy by self-propagating high temperature synthesis

Abstract

Porous NiTi shape memory alloy was fabricated by self-propagating high temperature synthesis. Effects of solution treatment under load applied on the microstructure were investigated. The densities of the phases changed insignificantly with solution treatment but the intermetallic phases such as Ti₂Ni, Ni₄Ti₃ and Ni₃Ti₂ disappeared and the density of B2(NiTi) phase increased with the load applied during solution treatment. Consequently, porous NiTi SMA with ideal pore characteristics, high chemical homogeneity and high strength for hard tissue implants was obtained.     

Process and compressive properties of porous nickel materials

Abstract

Compressive properties are investigated for the porous Ni materials processing by innovated powder metallurgical (PM) method. The porous Ni materials first show a short elastic region, then a long and oblique stress yield region within the strain range of about 10–50%, and finally, a densification region where the stress increases rapidly.     

Effect of Al2O3 and B4C particle additions on microstructure of PM copper based brake linings

Abstract

This paper highlights the effect of different ceramic particles on the structure of PM copper based brake linings. The copper based brake linings using a range of ceramic additives (1–6 wt-%) were prepared by powder metallurgy (PM). The optimum conditions for the production of brake linings were determined as compaction under 400 MPa and sintering at 805°C for 20 min in an argon atmosphere. The density of copper based brake linings decreased after sintering with the increase in ceramic powder contents for both Al₂O₃ and B₄C ceramic particles. The microstructural characterisation of produced samples showed that the lower boiling point elements in the as supplied powder vaporise during sintering from the structure and this leads to an increase in the porosity amount of the final component.     

Effect of pulsed current on reactively synthesised TiB2 consolidated by plasma pressure compaction

Abstract

The effect of pulsed current on TiB₂ formed by reactive consolidation between titanium and boron is reported in this paper. This consolidation was performed using the plasma pressure compaction (P²C) technique. A comparison between the pulsed and control samples reveals that pulsed current reduces grain growth (pulsed samples had an average grain size of 2·79 μm compared to 5·99 μm) while increasing sintering rates (pulsed samples were on average 15·5% more dense). The reduced grain growth and increased densification is due to the removal of adsorbed oxygen from the surface of the powder.     

Role of reinforcement in sintering of SiC/316L stainless steel composite

Abstract

Austenitic stainless steels with improved corrosion resistance are gaining wide popularity. However, their applications are limited because of their poor tribological properties. The present work was undertaken to improve the overall performance of 316L stainless steel by reinforcing it with SiC. During the processing of the 316L SS composite, the 316L SS matrix was found to interact strongly with the SiC at 1100°C resulting in the formation of low melting Fe–SiC phase. An attempt to process SiC/316L SS composite above this temperature resulted in complete melting of the composite compact.     

Behaviour of metal powders during cold and warm compaction

Abstract

An instrumented die was used to investigate the behaviour of metal powders during cold (ambienttemperature) and warm (up to 140^°C) compaction. This instrument enables simultaneousmeasurement of density, die wall friction coefficient, the triaxial stresses acting on the powderduring the course of compaction and ejection pressure. Commercial iron, titanium, aluminium,316L stainless steel (SS) and aluminium–silicon powders were employed for investigation. Theresults demonstrated the advantages of powder preheating on the compaction behaviour of metalpowders concerning green density, dimensional changes, frictional behaviour, ejectioncharacteristics and compactibility. However, the outlines also determined that the response ofthe non-ferrous powders to powder preheating is somehow different from those of the ferrouspowders. In this context, the behaviour of prealloy aluminium–silicon powders during compactionwas found of particular interest, as their compactibility is strongly affected by powder preheating,whereas the dimensional changes after ejection decrease considerably. This article presents theeffect of cold and warm compaction on the consolidation and ejection characteristics of ferrousand non-ferrous metal powders. The influence of compaction condition (pressure andtemperature) with considering of the powder characteristics and densification mechanisms areunderlined.     

Strain hardening behaviour of powder metallurgy alloys

Abstract

A model to describe the strain hardening behaviour of porous alloys, produced by powder metallurgy, is presented. It accounts for the influence of the matrix strain hardening ability, the initial porosity content and the pore geometry, and its predictive ability is verified with reference to sintered iron and an Fe–0·3%C sintered alloy. The necessity to introduce in the model a parameter able to account for the internal notch strengthening effect exerted by pores is emphasised. This parameter is found to be dependent on the sintering degree of the materials.     

Separation of copper from steel

Abstract

Copper has been separated from iron and steel by chlorine–air mixtures at 800°C. It was found that, contrary to predictions based upon thermodynamics, cupric chloride was the favoured copper product rather than cuprous chloride. This was due to the high vapour pressure of cupric chloride. It was found that in order to prevent the reaction between iron and cupric chloride it was necessary to preoxidise the iron to form an impervious oxide film. Copper contents lower than 0·05 wt-% were readily obtained after 10 min exposure to the gas, even when starting with several per cent of copper mixed with the iron or steel.     

Injection moulding of oxide reduced copper powders

Abstract

Fine oxide reduced copper powders of about 10 μm mean grain size are irregular in particle shape and high in oxygen content, which poses a difficulty in achieving good properties from injection moulding. Injection moulding was possible when a multicomponent binder with a large fraction of the backbone polymer was used. Injection moulded parts could be sintered to a density of about 95% theoretical, if reduction of the residual oxides in the powder was effectively carried out prior to closure of pores during sintering. Under such a condition, the injection moulded parts could attain an electrical conductivity higher than 80% of pure copper. July 2004.     

Mould lubrication and friction behaviour with hydraulic oscillators in slab continuous casting

Abstract

It is very important to obtain reliable lubrication from casting powder both at the meniscus and in the gap between strand and mould as it affects slab surface quality and caster productivity. With knowledge of mould friction, a quantitative insight into the behaviour of powder during caster operation is possible. In the present research, the friction was studied based on a slab continuous caster equipped with hydraulic oscillators. The effects of mould oscillation and the abrupt change of casting speed on mould friction force were evaluated, and the characteristics of lubrication behaviour in a casting sequence were investigated. In particular, a comparison between the mould friction force between sinusoidal oscillation mode and non-sinusoidal oscillation mode was made. Finally, the characteristics of friction before a breakout are discussed. The experimental and analytical results may contribute to the development of mould friction online measurement and more clearly learn the lubrication behaviour in different conditions.     

Experimental investigation of yield behaviour of metal powder compacts

Abstract

In this paper the compaction and yield response of two steel and two copper powders are examined. These were chosen to determine how the material response depends on the type of material and the morphology of the powder particles. Experiments were conducted in a computer controlled triaxial cell. Here, concentration is on the response during simulated, frictionless closed die compaction, whereby the radial stress is controlled so as to keep the radius of the sample constant. The compaction process was stopped at regular intervals and a series of probing paths were followed in stress space to construct the yield surface for the compact.

The experimentally determined yield surfaces are compared with yield surfaces predicted by empirical models and micromechanical models of the Fleck type, which assume that the compact consists of monosized spherical particles. During the early stages of compaction the form of the yield surfaces for spherical powders are consistent with Fleck's micromechanical model, but the surfaces become less elongated in the direction of loading at high densities. The yield surfaces for irregular shaped powders are significantly different from the predictions of the Fleck micromechanical model. A modified anisotropic Cam-Clay model is proposed, which is able to predict yield surfaces for the four powders at all densification levels.     

Influence of cooling and reheating on the evolution of copper rich liquid in high residual low carbon steels

Abstract

This study investigates some effects of austenite microstructure on processes leading to copper hot shortness. Low carbon steels containing 0˙55 wt-% copper were subjected to two thermal profiles in an infrared image furnace with attached confocal scanning laser microscope: hold at 1150°C for 60 s; hold at 1150°C for 60 s, quench to 400°C, reheat to 1150°C. Heat treatments were conducted in dried/deoxidised argon to image microstructures. Subsequent samples were oxidised in air. The oxide/metal interface was studied in a scanning electron microscope. Additional confocal scanning laser microscope experiments involved melting copper directly on the steel. After quench/reheat, austenite grain size decreased by a factor of ～1˙7 and grain boundaries were redistributed. Copper evolved during the first heating was no longer found at boundaries. Results from direct copper exposure reveal an apparent effect of boundary character on copper penetration rate. Possible mechanisms by which hot shortness is affected are discussed.     

Viscoelastic behaviour of porous sintered steels compact

Abstract

This paper describes the viscoelastic behaviour of sintered steels with porosities of 12, 20 and 33%, using a dynamic mechanical analyser. Test specimens were prepared from premix powders of 100–150 μm size by a process of die compaction, delubrication and sintering. The influences of test temperature and vibrational frequency on storage and loss modulus and tangent delta have been investigated. The investigated operating temperature and frequency was varied from 25 to 280°C and from 10 to 50 Hz respectively.     

Wear behaviour of Fe3 Al intermetallic particle reinforced PM based iron metal matrix composites

Abstract

The wear behaviour of unreinforced and reinforced PM based iron metal matrix composite, the latter containing 10 and 20 vol.-% nano sized Fe₃Al intermetallic particles, was studied as a function of sliding distance under two different loads and dry lubricated conditions. The intermetallic Fe₃Al nanoparticles were prepared by mechanical alloying and used as particle reinforcement with 10 and 20 vol.-% in the matrix. The processing of the composites included mixing and cold compaction followed by sintering at 1120°C. The influence of Fe₃Al additions on the dry sliding wear behaviour was studied at loads 20 and 40 N over sliding distances 2160, 3240, 4320 and 6480 m. The study showed that the composite exhibited a lower wear rate than that of the unreinforced matrix and the wear rate was influenced by the volume percentage of Fe₃Al particles. It is understood that iron aluminide reinforcement has a beneficial effect on the wear properties. Delamination and microcutting were the chief mechanisms of wear for the composites.     

凝胶注模法制备多孔铝铜合金

通过凝胶注模工艺,采用非水基凝胶体系,成功地制备了铝铜合金多孔材料.通过预备试验优化工艺,采用球磨的混粉手段,球料比为1:4,球磨时间30 min,非永基凝胶体系采用1 ml单体(HEMA),8 ml溶剂(PBO),0.2 ml交联剂(DEGDA),0.02 ml催化剂-引发剂(DMA-CHP),1.2g分散剂(PVP).研究不同烧结工艺参数对材料性能的影响.结果表明,在不添加发泡剂的前提下,烧结温度660℃时,烧结体的孔隙率为42.8％.烧结体中形成的第二相CuAl2,经过热处理后可使显微硬度明显提高,最大硬度可以达到95 HV.     

Development and characterisation of direct laser sintering multicomponent Cu based metal powder

Abstract

Recent advances in direct metal laser sintering (DMLS) have improved this technique considerably; however, it still remains limited in terms of material versatility and controllability of laser processing. In the present work, a multicomponent Cu based metal powder, which consisted of a mixture of Cu, Cu–10Sn and Cu–8·4P powder, was developed for DMLS. Sound sintering activities and high densification response were obtained by optimising the powder characteristics and manipulating the processing conditions. Investigations on the microstructural evolution in the laser sintered powder show that liquid phase sintering with partial or complete melting of the binder (Cu–10Sn), but non-melting of the cores of structural metal (Cu) acts as the feasible mechanism of particle bonding. The additive phosphorus acts as a fluxing agent to protect the Cu particles from oxidation and shows a concentration along grain boundaries owing to the low solubility of P in Cu and the short thermal cycle of laser sintering. A directionally solidified microstructure consisting of significantly refined grains is formed, which may be ascribed to laser induced non-equilibrium effects such as high temperature gradient and rapid solidification.     

Cold model study of metal droplet descent through fluids including a treatment of the non-Newtonian behaviour as exhibited by molten slag system

Abstract

In the context of several high temperature metallurgical processes including blast furnaces, a cold model study simulating a metal droplet descent through the surrounding fluid system is presented. The study comprises an experimental programme employing wide range of fluids exhibiting both Newtonian and non-Newtonian behaviour. Such fluid systems are encountered in slag–metal droplet systems where viscosity of the slag system has a significant effect on the kinetics of refining reactions. Slag systems generally possess random network structures comprising internal regions of weak ordering and the presence of these regions may result in non-Newtonian behaviour of the slag. As the viscosity of the slag is very sensitive to structure, a treatment of non-Newtonian behaviour as exhibited by some molten slag systems is therefore required. Two parameters have been identified and estimated that help to determine the rheological characteristics of fluids in relation to their network structure. The underlying principle of the model development has been that the external pressure exerts a driving force that affects the motion of the fluid to a degree dependent on the rheological behaviour and the network structure of the fluid. The paper also describes some results of a cold model study of the momentum transfer to the fluid system by correlating the drag Reynolds number with the modified drag coefficient for non-Newtonian fluids

(N*_Rem)^½?n′ = (N _Rem)^½?n′ (1/2C _Dm )^½     

Some data on the infiltration of porous iron-manganese alloys with copper and its alloys

Summary It is clearly shown that nonporous iron-manganese-copper alloys can be produced by infiltrating an iron-manganese matrix with copper or copper alloys.Additional data have been obtained on the effectiveness of copper, a copper-manganese master alloy, and brass as infiltrating materials; the feasibility of producing a nonporous iron-manganese alloy free from oxide inclusions is demonstrated.Data are presented on the formation of iron-manganese-copper alloys with different manganese contents during infiltration with copper and copper-manganese master alloys, under different infiltration conditions.The extent of phase interaction during infiltration and the condition of boundaries in alloys produced under different infiltration conditions have been investigated.     

铜基高通量换热管内多孔层的制备及性能研究

烧结型高通量换热管是通过在普通换热管内表面烧结一定厚度的多孔金属层达到强化沸腾传热的效果,多孔层的烧结温度对基管性能不能有损伤,同时要求多孔层本身孔隙连通,与基管结合较好,且耐蚀性与基管相当。本文设计了一种适用于铁白铜基管（BFe10-1-1）的管内多孔层烧结合金粉末Cu-10% Ni-20% Zn-2% Sn（质量分数）,该粉末成分耐蚀性优于基管。烧结实验结果表明,该合金粉末在940℃下烧结时对基管性能无损伤,烧结后与基管结合良好,同时粉末多孔层内部孔隙均匀联通;进一步的应用实验也证明,该多孔层合金粉末具有非常好的传热效果。