Fabrication of in situ TiB2–TiC reinforced steel matrix composites by spark plasma sintering

Abstract

In situ TiB₂ and TiC particulates reinforced steel matrix composites have been fabricated using cheap ferrotitanium and boron carbide powders by spark plasma sintering (SPS) technique. The sintering behaviour and the formation mechanism of the composite were studied. The results show that when the composite was sintered at 1050°C for 5 min, the maximum relative density and hardness of the composite are 99·2% and 83·8 HRA respectively. The phase evolution of the composite during sintering indicates that the TiB₂ and TiC reinforcements were formed in situ as follows: first, the solid/solid interface reaction between Fe₂Ti and B₄C, resulting in the formation of a small amount of TiB₂ and TiC below 950°C; second, the solid–liquid solution precipitation reaction in the Fe–Ti–B–C system, resulting in the formation of the main TiB₂ and TiC reinforcements at ～1000°C.     

Structural heterogeneity and its effects on the properties of an in situ TiB2–TiC/Cu composite synthesised by hot pressing

ABSTRACT

In situ TiB₂ and TiC reinforced copper matrix composites with tailored heterogeneous structure were fabricated via high-energy ball milling of Cu, TiH₂ and B₄C powders followed by hot pressing. The microstructures of both ball-milled powders and hot-pressed composites were compared. Although the dislocation density of Cu matrix was changed after hot pressing, the mode of distribution of ceramic phases in the Cu matrix was noted to transmit from the ball-milled powders to hot-pressed composites in case of the TiH₂ particles synthesised by the in situ reactions. The structural inheritance between the ball-milled powders and hot-pressed composites could be used to control microstructural features and thus to tune properties. The hot-pressed TiB₂–TiC/Cu composites with tailored heterogeneous structure exhibited better performance than those of homogeneous counterparts.     

Combustion synthesis of Fe–Al/TiC composite powders and effect of Al content on its characteristics

Abstract

In this work, combustion synthesis of ferrotitanium–Al–C powder mixtures with different compositions was carried out to synthesise Fe–Al/TiC composites. Differential thermal analysis was performed on the precursor powder from ambient temperature to 1673 K at a heating rate of 30 K min^?1. Phase development and structural changes were investigated by X-ray diffraction technique and scanning electron microscopy. The results showed that no trace of TiAl_x (x?=?1, 3) was formed in all samples, and the reaction of (Ti–Fe)–Al–C system took place in the following two steps: first, molten Al and Fe reacted exothermically to form Fe–Al intermetallic compound. Second, the produced heat melted the ferrotitanium with lower Fe content and resulted in a liquid containing Ti, Fe, Al and C. TiC formed in all samples, but depending on the Al content, different phases containing FeAl₂, FeAl, Fe₃Al, Fe₃AlC_x and α-Fe formed as phases of matrix. The mixture with the lower Al content gave out a higher combustion temperature.     

Effect of separate and combined milling of Cu and TiB2 powders on the electrical and mechanical properties of Cu–TiB2 composites

The present work compares the properties of the Cu–TiB₂ composites prepared by varying the mechanical milling conditions. The Cu–TiB₂ composites were processed using Cu–TiB₂ powders combined milling, a powder mixture consisting of separately milled Cu & TiB₂ and a powder mixture prepared by the combination of separate and combined milling. The hardness and flexural strength of the combined milled powders were found to be maximum, despite of their lower sintered density. The separately milled powders achieved excellent electrical properties combined with moderate hardness and flexural strength. The properties of composites processed using the combination of separate and combined milling laid in between the two conditions of combined and separate milling.     

Synthesis and Characterization of Ti/(TiB + TiC) Hybrid in-situ Composites by Spark Plasma Sintering

Since Ti alloys exhibit inferior wear resistance and suffer considerable loss in mechanical strength at high temperature, it is aimed at synthesis an in-situ Ti/(TiB + TiC) hybrid composite. In order to synthesis Ti/(TiB + TiC) in-situ composite, B₄C particulate was mixed with titanium powder and sintered at 1400 °C at different time intervals by spark plasma sintering. Sintering parameters were optimized according to the complete in-situ reactions. Density of the sintered compacts was measured by Archimedes principle. Energy dispersive spectroscope and optical microscope observations of the sintered samples revealed that with increasing sintering time TiB and TiC particulates were gradually transforming into needle like structure and near equiaxed structure, respectively.     

Synthesis of Ni–TiC Composite by Ball Milling and Heat Treatment of NiO/TiO2/C Powder Mixture

In this study, a Ni–TiC composite was synthesized by the carbothermic reduction of activated NiO/TiO₂/C powder mixture. The effect of 0-, 2-, 5-, and 10-h ball milling of the sample on the reduction process was investigated. Results of XRD pattern from milled samples showed that no reaction occurred between NiO, TiO₂, and carbon due to milling. FESEM images for samples milled for 2, 5, and 10 h revealed the fine distribution of the brittle oxide particles in the matrix of graphite, as a ductile phase. Particle size reduction was also noticeable, especially in the case of oxide particles. By increasing the milling time, agglomeration of particles was also observed. Results of the thermogravimetry analysis of milled and un-milled mixtures showed the onset temperature of reduction for NiO decreased from 867 °C in the un-milled sample to 582, 571, and 560 °C in samples activated for 2, 5, and 10 h, respectively. Also, the onset temperature of the reduction of TiO₂ decreased from 1029 for the sample milled for 2 h to 1019 and 1004 °C for samples milled for 5 and 10 h, respectively. The XRD pattern of the heat-treated milled powder mixture for 1 h under vacuum proved that Ni–TiC composite was formed at 1100 °C. It was found that bulk Ni–TiC composite could be synthesized by the heat treatment of activated powder at 1300 °C. Formation of TiC quadrilateral particles as reinforcement in the continuous matrix of Ni was evident at this temperature. Furthermore, the best morphology with the most appropriate particle size distribution was observed in the sample milled for 2 h.

     

Microstructural studies of W – Cu nanostructured precursor composite powders prepared by mechanical alloying

Abstract

The present work reported the fabrication of the W–Cu nanocomposite precursor powders via high energy ball milling. The W–25 wt-%CuO powders were taken as the raw materials, and the following process condition was used: ball to powder weight ratio of 20 : 1, the rotation speed of 500 rev min^&minus1, the milling time of 15–45 min and 1–40 h, and the mode of milling 10 min, air cooling 30 min. The phase and microstructure of the as milled powders with variation of milling time was investigated, using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The experiment results show that the nanocomposite powders can be successfully synthesised by mechanical alloying using a short time of 1 h. During the ball milling, CuO powders were reduced by W, and a portion of the W powders were oxidised into WO_x (x=2 to 3). The possible mechanism of the reaction was detected.     

The influence of milling parameters on the characteristics of milled and spray-dried NiCoCrAlY–Al2O3 composite powders

Spray-drying process was selected to agglomerate ball milled NiCoCrAlY–Al₂O₃ composite powders. The effect of the starting alloy powder size on the morphology of composite powder was studied. The parameters of milling were optimised by orthogonal experiment to improve the powder’s flowability and apparent density. Then the optimised powder was sprayed by air plasma spray to prepare NiCoCrAlY–Al₂O₃ composite coating. The results showed that the size distribution of starting particles decided the deformation of alloy particles and the characteristics of agglomerated powders eventually. With the decreasing size range of the starting alloy particles, the sphericity of agglomerated powders increased. The optimised milling parameters were as follows: solid content, 60?wt-%; BPR, 4:1; the rotating speed, 350?rev?min^?1; and milling time, 5?h. And the contribution of solid content was the largest. The Al₂O₃ splats showed good adhesion with alloy matrix when the composite powder melted in good condition.     

Structure of electroexplosive TiC–Ni composite coatings on steel after electron-beam treatment

The phase and elemental compositions of the surface layer in Hardox 450 steel after electroexplosive spraying of a TiC–Ni composite coating and subsequent irradiation by a submillisecond high-energy electron beam are studied by the methods of modern physical metallurgy. The electron-beam treatment conditions that result in the formation of dense surface layers having high luster and a submicrocrystalline structure based on titanium carbide and nickel are found. It is shown that electron-beam treatment of an electroexplosive coating performed under melting conditions leads to the formation of a homogeneous (in structure and concentration) surface layer.     

Synthesis of the ZrN–ZrB2 Composite by Spark Plasma Sintering

Powder Metallurgy and Metal Ceramics - Reactive spark plasma sintering of ZrH2, BN, and B powder mixtures in the temperature range 1500–1900°C was used to produce a ZrN–ZrB2...     

Comparative Study of Coatings formed by Electrospark Alloying Using TiC–NiCr and TiC–NiCr– Eu2O3 Electrodes

Russian Journal of Non-Ferrous Metals - Coatings formed on steel 40Kh by electrospark alloying (ESA) using TiC–NiCr and TiC–NiCr–Eu2O3 electrodes are investigated. The coatings...     

TiB2对TiC基金属陶瓷显微组织的影响

研究了TiB2对TiC基金属陶瓷显微组织的影响。试验发现1420℃下烧结90min后，TiC基金属陶瓷的硬质相颗粒明显长大。分析表明，TiB2在高温下能够与TiC基金属陶瓷中的Mo反应生成MoB，并主要分布于硬质相表面的环形相中。硬质相的长大可能与MoB导致的液相不足和硬质相颗粒接触长大有关。     

Processing and performance of Cr2O3–Fe2O3 reference electrode powders prepared by oxide coprecipitation

Abstract

Cr₂O₃–Fe₂O₃ based oxide mixtures for reference electrode powders of oxygen sensors were processed using oxide coprecipitation route. A special method for preparing reference electrode powders has been developed by mixing coarse Cr particles with the oxide mixture in the form of Cr–Fe hydroxide. Morphology and size of the mixed oxide powders were characterised by means of scanning electron microscopy and laser diffraction method. With the coprecipitation process, chemically homogeneous and very fine powders with a mean particle size of 1.53 μm were prepared. This powder mixture adhered and loosely coated to Cr particles. The processed reference electrode powders were tested in low level oxygen concentration measurements of steelmaking process under industrial scale. The reference electrode powders showed excellent results in terms of electromotive force reproducibility, response time and accuracy in soluble aluminium predictions at the oxygen concentration measurements. Most of the particles of the reference electrode powder remained separated after dipping to molten steel.     

Structure of the molybdenum–carbon–copper composite coatings produced by electroexplosive spraying followed by electron-beam treatment

Electroexplosive Mo–C–Cu composite coatings are modified by a high-energy electron beam for the first time. Our studies demonstrate that the electron-beam treatment of the electroexplosive spraying layer that is performed under melting conditions leads to the formation of a structurally and concentration homogeneous surface layer.     

Synthesis of TiC–NiCrBSi Binder Alloy Composite Powders for Cladding and Deposition of Wear-Resistant Coatings

Russian Journal of Non-Ferrous Metals - TiC–NiCrBSi binder metal matrix composites are fabricated by self-propagating high-temperature synthesis (SHS) in reaction powder mixtures of titanium,...     

Hot forging of Ti–6Al–4V alloy preforms produced by spark plasma sintering of powders

Abstract

Powder preform forging is a technology that comprises the preparation of near net shape preforms through powder metallurgy and a subsequent hot forging in order to obtain the desired final shape. In this work, two Ti–6Al–4V powder preforms were sintered through spark plasma sintering (SPS) and then hot compressed in a horizontal dilatometer. Varying the temperature of the process, two full density preforms having different microstructures were produced: sintering at 950°C, a plate-like α was obtained, whereas sintering at 1050°C, an acicular α was obtained. The behaviour of the preforms under hot forging has been studied through hot compression tests carried out in a quenching and deformation dilatometer in a range of temperature and strain rates typically used in hot forging this alloy (850–1050°C, 0·01–1 s^?1). Hot workability has been evaluated by measuring the stresses required for deformation and by analysing both the stress–strain curves recorded during testing and the microstructures after deformation. The main microstructural phenomena occurring during hot compression were individuated. The best conditions for the hot forging operation of SPS preform are temperatures above β transus, where the materials are deformed in a regime of dynamic recrystallisation, at every strain rate.     

Self-Propagating High-Temperature Synthesis of (Al–2% Mn)–10% TiC and (Al–5% Cu–2% Mn)–10% TiC Nanostructured Composite Alloys Doped with Manganese Powder

Russian Journal of Non-Ferrous Metals - The influence of alloying with powder manganese on the preparation of nanostructured (Al‒2% Mn)–10% TiC and (Al–5% Cu–2%...     

TiC,TiN,TiB2的主要性质和合成方法

本文介绍了ＴｉＣ，ＴｉＮ和ＴｉＢ２的主要物理性质，合成ＴｉＣ，ＴｉＮ和ＴｉＢ２的基本原理和主要工艺条件。