Microstructure Characteristic of In-situ Ti/TiC Composites

TiC reinforced titanium composites has been produced with different Al content and C content by XDTM. The results have shown that TiC particles are of two different morphologies f coarse dendritical primary TiC and short bar-shape eutectic TiC. Al content has great effects on the morphology of TiC. With the increasing of Al content, the morphology of primary TiC changes from coarse developed dendrite into short bar-shape or plate--shape TiC with 35%Al. Meanwhile, the structure of the matrix changes from single Ti to Ti and Ti2Al and to Ti3Al. However, the C content has no influence on the microstructure of matrix. When the C content is less than 1.2%, the dendrite TiC disappears and only short bar-shape or plate-shape TiC exists in the composites. In addition, the effect of heat of heat treatment on the morphology of TiC has also studied.     

In situ formation of TiC particulate composite layer on cast iron by laser alloying of thermal sprayed titanium coating

Commercial flake graphite cast iron substrate was coated with titanium powder by low pressure plasma spraying and was irradiated with a CO₂ laser to produce the wear resistant composite layer. The macro and microstructural changes of an alloyed layer with the traveling speeds of laser beam, the precipitate morphology of TiC particulate and the hardness profile of the alloyed layer was examined. From the results, it was possible to composite TiC particulate on the surface layer by direct reaction between carbon existed in the cast iron matrix and titanium with thermal sprayed coating by remelting and alloying them using laser irradiation. The cooling rate of the laser remelted cast iron substrate without a titanium coating was about 1 × 10⁴ K/s to 1 × 10⁵ K/s in the order under the condition of this study. The microstructure of the alloyed layer consisted of three zones; the TiC particulate precipitate zone (MHV 400–500), the mixed zone of TiC particulate + ledeburite (MHV 650–900) and the ledeburite zone (MHV 500–700). TiC particulates were precipitated as a typical dendritic morphology. The secondary TiC dendrite arms were grown to a polygonized shape and were necking. Then the separated arms became cubic crystal of TiC at the slowly solidified zone. In the rapidly solidified zone near the fusion boundary, however the fine granular TiC particulates were grouped like grapes.     

自生TiC增强钛基复合材料的微观组织

采用反应自生法制备了ＴｉＣ颗粒增强钛合金基复合材料,研究了复合材料的相组成和微观组织。在Ｔｉ－６Ａｌ－２Ｃ合金中存在Ｔｉ和ＴｉＣ两种相。ＴｉＣ权树枝状初生Ｔｉｃ和短棒状共晶ＴｉＣ两种开头存在,其中共晶ＴｉＣ主要存在于晶界,特别是三角晶界处。ＴｉＣ晶格常数的计算结果表明ＴｉＣ的衍射峰存在一定的偏移,主要是由于存在于ＴｉＣ中的Ｃ空位引起晶格畸变。随着Ａｌ含量的增加,初生ＴｉＣ由发达粗大的树枝晶变为不发达的树枝晶,当Ａｌ含量为３５％时变为短棒状和薄片状的ＴｉＣ。基体组织也相应地由单一的Ｔｉ基体变为Ｔｉ和Ｔｉ３Ａｌ的两相基体以及Ｔｉ３Ａｌ和ＴｉＡｌ两相基体。根据相图分析了组织变化的主要原因。     

Effect of cerium addition on microstructures of carbon-alloyed iron aluminides

The effect of Ce addition on the microstructure of carbon-alloyed Fe₃Al-based intermetallic has been studied. Three different alloys of composition, Fe-18.5Al-3.6C, Fe-20.0Al-20C and Fe-19.2Al-3.3C-0.07Ce (in at%), were prepared by electroslag remelting process. Their microstructures were characterized using optical and scanning electron microscopies. Stereological methods were utilized to understand the observed microstructures. All the alloys exhibited a typical two-phase microstructure consisting of Fe₃AlC carbides in an iron aluminide matrix. In the alloy without Ce addition, large bulky carbides were equally distributed throughout the matrix with many smaller precipitates interspersed in between. In the alloy with Ce addition, the carbide grain sizes were finer and uniformly distributed throughout the matrix. The effect of Ce addition on the carbide morphology has been explained based on the known effect of Ce in modifying carbide morphology in cast irons.     

钛合金中TiC在高温处理过程中形态变化机制

钛合金中的TiC颗粒形态复杂,尺寸大,不利于合金性能的提高.适当的高温处理工艺可改变TiC/Ti合金中TiC形态和尺寸,本文对不同成分合金在不同高温处理条件下的形态变化规律的详细研究结果表明,当高温处理温度及碳元素在基体中的固溶度不同时,TiC形态变化机制也不相同,因此总结分析的基础上提出两种TiC形态变化机制,即溶解-析出机制和溶解-固溶-脱溶机制,并理论上详细研究和分析了各种机制下,TiC形态、尺寸变化的原因及机理.     

Microstructural characteristics of TiC and (TiW)C iron matrix composites

The present work investigated microstructures of in situ synthesized 10 vol% TiC-Fe and 10 vol% (TiW)C-Fe composites. The results show that in the TiC-Fe composite, as only second phase, TiC is in two kinds of morphologies, i.e., spherulic and rod-like ones. It is thought that the spherulic TiC is a proeutectic phase and the rod-like one is a eutectic phase. In situ synthesis of the 10 vol% (TiW)C-Fe composite in liquid iron is feasible. In the composite, the (TiW)C reinforcements as only one second phase are more homogeneously distributed in iron matrix, and most of them are spherulic and the few rod-like. Within the spherulic (TiW)C phase, there is an inhomogeneous distribution of titanium and tungsten. Its core is rich in titanium, while the periphery rich in tungsten. Such the characteristic microstructure is closely related with its formation during solidification. Comparing with the TiC, the (TiW)C phase has a density matchable for iron melt, which makes it more suitable as in situ synthesized reinforcements in large size ingots of iron matrix composites.     

碳含量对自生TiC_P增强钛基复合材料组织的影响

采用反应自生法制备了 Ti C颗粒增强钛合金基复合材料 ,并通过 XRD,SEM对复合材料的相组成和微观组织进行了研究。结果表明 :在 Ti- 6Al- 1 .8C中主要存在 Ti和 Ti C两种相。Ti C以树枝状初生 Ti C和短棒状共晶 Ti C两种形态存在。对 Ti C晶格常数的计算结果表明 ,Ti C的衍射峰存在一定的偏移 ,主要是由于 Ti C中存在 C空位。研究了 C含量对材料组织和 Ti C形貌的影响。结果表明 :C含量对基体组织基本没有影响 ,但是随着 C含量由 1 .98%减少到 0 .39% ,粗大的树枝状 Ti C逐渐消失 ,Ti C以短棒状为主 ,部分呈羽毛状。     

Microstructural assessment of interaction zone in titanium aluminide/TiC metal matrix composite

Abstract

Samples of Ti–24Al–11 Nb/TiC composites were heat treated at temperatures between 1000 and 1200°C for several hours and the extent of the reaction zone between the Ti–24Al–11Nb matrix and the TiC particulate was assessed using optical, scanning electron, and analytical transmission electron microscopy. It has been shown that there is an interaction zone surrounding each TiC particle caused by the diffusion of C from the TiC into the matrix and diffusion of Nb into the TiC. The extent of these interactions increases with increase of time and increase of temperature. The phases formed during heat treatment were shown to be Ti₃(AlNb)C and (TiNb)C. The significance of these observations is briefly discussed in terms of recent work in which it has been shown that there is no detectable change in the matrix in similarly treated Ti–6AI–4V/TiC composites.

MST/946     

Casting of TiC-Reinforced Steel Matrix Composite

Titanium carbide varying from 6.34 to 21.60 volume fraction was reinforced in to iron matrix by the direct reaction of pure titanium in molten Fe-C alloy. A simple casting technique has been developed successfully to improve the precipitation and distribution of titanium carbide particles in iron matrix. Lime powder is used as a protective layer on the molten metal to avoid oxidation of titanium during melting and casting. The thermodynamic and kinetic studies support the precipitation of TiC in molten Fe-C alloy at the reaction temperature, 1600°C. The size and shape of the in-situ TiC particles depend on the amount of titanium present in Fe-C molten alloy.     

激光熔化沉积(TiB+TiC)/TA15原位钛基复合材料的显微组织与力学性能

利用激光熔化沉积工艺制备了TiB+TiC增强相体积分数分别为9%、11%、22%及57%的4种(TiB+TiC)/TA15原位钛基复合材料。随增强相含量提高,TiB形态由片层状向棱柱状转化,TiC形态由不规则颗粒状向枝晶状转化,钛基复合材料硬度及弹性模量均显著提高而塑性明显下降。增强相体积分数约为9%的复合材料表现出较好的综合力学性能,增强相体积分数大于11%后复合材料的抗拉强度急剧降低。与激光熔化沉积态TA15钛合金相比,TiB+TiC增强相体积分数约为9%的复合材料抗拉强度（1040 MPa）及屈服强度（935 MPa）均提高约12%。      

Effect of morphology of second-phase martensite on tensile properties of Fe-0.1C dual phase steels

Fe-0.1 C steel has been studied to determine the effect of morphology (shape, size and distribution) of the second-phase martensite on the tensile properties of dual phase steels. Retention at an intercritical temperature of 1023 to 1073 K followed by ice-brine quenching (intercritical quenching treatments), whereby martensite appears to surround the ferrite grain, increased strength, but produced an increased yield ratio and decreased ductility. Incorporation of 1223 K direct ice-brine quenching prior to the intercritical quenching treatment at 1053 K gave rise to the distribution of fine spheroidized martensite in a refined ferrite matrix. The heat treatment significantly improved strength and ductility, but produced a somewhat increased yield ratio. Austenitization at a temperature of 1223 K followed by step quenching to 1023 K prior to ice-brine quenching, whereby martensite was randomly scattered in massive form in the ferrite matrix, gave a better combination of strength and ductility and produced a decreased yield ratio. These results are briefly discussed in terms of stress-strain analysis and fractography.     

TiB2 and TiC stainless steel matrix composites

Stainless steel matrix composites reinforced with TiB₂ or TiC particulates have been in situ produced through the reactive sintering of Ti, C and FeB. X-ray diffraction analysis confirmed the completion of reaction. The TiB₂, TiC and steel were detected by X-ray diffraction analysis. No other reaction product or boride was found, indicating the stability of TiB₂ and TiC in steel matrix. The SEM micrographs revealed the morphology and distribution of in situ synthesized TiB₂ and TiC reinforcements in steel matrix. During sintering the reinforcements TiB₂ and TiC grew in different shapes. TiB₂ grew in hexagonal prismatic and rectangular shape and TiC in spherical shape.     

Investigation on the Fe-based PM materials reinforced by In Situ synthesized TiC particulates

Atomized iron powder, carbonyl nickel powder, molybdenum powder, electrolytic copper powder, titanium powder and graphite powder were used as experimental materials; the titanium and graphite powders were added by an atomic ratio of Ti/C = 1:1 (the addition of Ti was 0 ～ 4 wt%) to Fe-2Ni-0.5Mo-2Cu-0.3C powder, and the iron-based powder metallurgy materials reinforced by in situ-synthesized TiC particulates were prepared by a powder metallurgy technique. The results show that the microstructures of sintered samples are mainly pearlite, ferrite and bainite. The amount of pearlite increases with the increase of Ti content, whereas the ferrite and bainite decrease. TiC particles sized 0.3 µm distribute mainly near the grain boundary of pearlite. The apparent hardness of sintered samples increases, while the sintered density and flexural strength decrease with the increase of Ti content. The fracture morphology of the sintered materials is brittle type.     

Reactive sintering mechanism of Ti + Mo<Subscript>2</Subscript>C and Ti + VC powder compacts

TiC reinforced Ti-matrix composites have been synthesized successfully by reactive sintering of Ti-1.5%Fe-2.25%Mo (wt%) powder compacts with addition of Mo₂C and VC particles. The reactions for the formation of TiC particles start at 600 °C, but the distribution of TiC particles and the densification behavior in the two compacts are significantly influenced by the metal carbides (Mo₂C or VC). The compact with addition of Mo₂C has a relative density of 98% after sintering at 1300 °C for 1.5 h, but TiC particles are agglomerated in the Ti matrix. The compact with addition of VC has a relative density of about 91% after sintering at 1300 °C for 1.5 h, but TiC particles distribute more homogenously in the Ti matrix. Different TiC particle distribution and densification behaviors are attributed to the reaction rates between Ti and metal carbides and the subsequent diffusion process.     

A Metallographic Study of the High-Temperature Decomposition of Austenite in Alloy Steels Containing Mo and Cr

Optical and electron microscopy have been used to study the complex microstructures developed during the isothermal decomposition of austenite above 550°C in Fe-4Mo-0.2C and Fe-10Cr-0.4C alloy steels. As the transformation temperature is decreased, the decomposition products change from the disordered growth of nodular alloy pearlites to blocky ferrite structures containing fine dispersions of alloy carbide, and finally to acicular ferrite structures also containing alloy carbide. The branched M₆C and M₂₃C₆ of the high-temperature pearlite is replaced by Mo₂C and M₇C₃ with a fibrous or lath morphology in the lower temperature structures. The decomposition microstructures are explained in terms of a model which takes account of the growth of particular alloy carbides at the interfaces of ferrite allotriomorphs, where the growth mechanism, and hence the morphology, is sensitive to transformation temperature.     

Microstructure of XDTM Ti-6Al/TiC composites

XD^TM method has been used to prepare TiC particles reinforced titanium composites. The phases constitute and microstructure of the Ti-6Al/TiC composites have been investigated by XRD and SEM. The lattice parameter value of TiC calculated from the XRD pattern has indicated that there exists carbon deficiency in TiC. The microstructure observed by SEM has shown that TiC is of dendritical and spherical morphology, which quite different from that of the TiC in Al/TiC master alloy. In macrostructure, the TiC particles homogeneously distribute in the matrix, but the spherical TiC mainly segregate at the grain boundary, especially at the triangle grain boundary. Microstructure of the interface has also been observed by TEM and HTEM. No reaction product has been found in the interface, but a C atom diffusion layer was determined by energy spectrum diffraction and observed by HREM image of interface microstructure. Although no definite crystallographic relationship can be defined, a orientation relationship of [0110]_Ti//[011]_TiC has been obtained.     

Electrochemical and microstructural studies of sintered and sintered-plasma nitrided steel containing different alloying elements

The corrosion of sintered and sintered-plasma nitrided steels containing different alloying elements was evaluated through analysis of the potentiodynamic polarization curves of the samples at pH = 7, with 1.25 M KNO₃ as electrolyte. The Fe-3.0% Ni and Fe-0.1% C sintered alloys show better performance in relation to electrochemical corrosion, than sintered pure iron samples. In addition, Fe-4.0% Mn, Fe-1.5% Mo and Fe-1.5% Si alloys exhibited increased anodic current densities in relation to the pure iron sample. After the nitriding process the anodic current densities of all samples containing an alloying element were considerably diminished. The sintered-nitrided pure iron sample was the only nitrided part whose current density was higher than the current density of the non-nitrided sample.     

Particulate migration behavior and its mechanism during selective laser melting of TiC reinforced Al matrix nanocomposites

A transient three-dimensional model for describing fluid flow characteristics and particles migration behavior within the melt pool during selective laser melting (SLM) of TiC/AlSi10Mg nanocomposites was developed. The powder-solid transition, variation of thermophysical properties, and surface tension were considered in the model. The influence of laser energy per unit length (LEPUL) on heat and mass transfer, melt pool dynamics, and particles rearrangement was investigated. It showed that the Marangoni convection became more vigorous with an increase of LEPUL, accordingly enhancing the thermal capillary force. The high laser energy input induced a sufficient liquid formation and an improved wettability, lowering the friction force exerting on TiC solids. Under this condition, the reinforcing particles can be well mixed within the matrix. The experimental study on the distribution state of TiC reinforcement in the SLM-processed Al matrix was performed. The results validated that the dispersion of TiC reinforcement changed from a severe aggregation to a uniform dispersion in the matrix with the increase of LEPUL. The TiC reinforcement experienced a microstructural variation from the standard nanoscale structure with a mean particle size of 70–90 nm to the relatively coarsened submicron morphology with an average particle size of 134 nm as LEPUL increased.     

Wear characteristics of TiC reinforced cast iron composites Part 2 – Abrasive wear

Abstract

The presence of carbide particles in metal matrix composites improves abrasive wear resistance properties. Abrasive wear characteristics of TiC reinforced cast iron composites have been investigated. The TiC particle size and distribution influence the wear properties of the composites. TiC reinforced cast iron composites possess better wear resistance properties than those of chromium cast irons with and without nitrogen.     

Changes in γ-TiC stoichiometry during heat treatment of TiC reinforced Ti composites

Abstract

A liquid phase technique (casting) has been successfully employed for the production of Ti/TiC in situ metal matrix composites. The γ-TiC phase produced by this process is highly substoichiometric. Changes in chemistry of the TiC phase in these composites are noted during annealing at elevated temperatures. The degree of stoichiometry of TiC increases during annealing at 1050°C and further during post-annealing aging at 750°C. This increase in the degree of stoichiometry (C/Ti atomic ratio) is accompanied by lattice expansion and reduction in microhardness values of the TiC particles. The change in TiC stoichiometry is accompanied by the precipitation of soft Ti particles within the TiC phase. The results are compared with those obtained from composites fabricated by a powder metallurgy route where the carbide chemistry is insensitive to heat treatment.