Instability of TiC and TiAl3 compounds in Al-10Mg and Al-5Cu alloys by addition of Al-Ti-C master alloy

The performance of Al-Ti-C master alloy in refining Al-10Mg and Al-5Cu alloys was studied by using electron probe micro-analyzer （EPMA） and X-ray diffractometer （XRD） analysis. The results indicate that there are obvious fading phenomena in both Al-10Mg and Al-5Cu alloys with the addition of Al-5Ti-0.4C refiner which contains TiC and TiAl3 compounds. Mg element has no influence on the stability of TiC and TiAl3, while TiC particles in Al-10Mg alloy react with Al to form Al4C3 particles, resulting in the refinement fading. However, TiC particles are relatively stable in Al-5Cu alloy, while TiAl3 phase reacts with Al2Cu to produce a new phase Ti（Al, Cu）2, which is responsible for the refinement fading in Al-5Cu alloy. These indicate that the refinement fading will not occur only when both the TiC particles and TiAl3 compound of Al-Ti-C refiner are stable in Al alloys.     

A1TiCCeP对Al-30％Si合金初晶硅相的变质效果研究

借助SEM与XRD分析手段,对自制的AITiCCeP（舍2％P）中间合金进行物相分析,并以Al-30％Si合金为变质对象,探讨其对初晶硅的变质效果与变质机理。结果发现：A1TiCCeP中间合金组织中含有TiC、AlP、TiAl3和Ti2Al20等物相,当A1TiCCeP的添加量（以磷的实际添加量计算）为Al-30％Si合金质量的0．15％时,对初晶硅变质效果显著,平均尺寸约为281zm,优于商用Cu．P中间合金。     

碳源对自蔓延高温合成TiC粉末的影响

在氩气保护下用钛、碳元素通过自蔓延高温合成(SHS)工艺制备了碳化钛,采用X射线衍射(XRD)和扫描电子显微(SEM)技术,分析检测了采用不同碳源合成的碳化钛的物相组成和微观结构.结果表明,钛与碳元素粉末的自蔓延合成产物均为碳化钛相,产物形貌因碳源的不同而有所不同,以石墨为碳源所合成的TiC晶型比较完整,粒度相对粗大、颗粒均匀性相对较好,团聚较少,更接近化学计量比.     

Ti-C-Al-Fe_2O_3反应体系的热力学及形成产物的分析

针对Ti-C-Al-Fe2O3体系进行了热力学计算,并结合DSC及XRD分析,为研究该体系反应合成TiC,Al2O3提供了理论依据.计算结果表明：该体系在发生SHS反应时,可以生成TiC,Al2O3,Fe2Ti,TiAl3,Fe3C和Al4C3等产物,但TiC,Al2O3的热力学稳定性要远远大于Fe2Ti,TiAl3,Fe3C和Al4C3等相,因此,在1600℃的钢液引燃的SHS反应过程中,只能生成TiC,Al2O3两种产物.通过XRD分析也证明了在反应产物中只有TiC,Al2O3两种物质形成.     

Dissolution-precipitation mechanism of self-propagating high-temperature synthesis of TiC-Cu cermets

The mechanism of self-propagating high-temperature synthesis (SHS) of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope (SEM) with energy dispersive X-ray (EDX) spectrometry, and the combustion temperature was measured. The results showed that the com- bustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solu- tion. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.     

Si和Al对机械合金化合成Ti3SiC2的影响

采用3Ti／Si／2C单质粉体为原料,进行机械合金化,以合成Ti3SiC2粉体。研究了Al和过量Si对机械合金化合成Ti3SiC2的影响。研究结果表明,机械合金化单质混合粉体,会诱发自蔓延反应。反应后产生大量坚硬的颗粒状产物。机械合金化3Ti／Si／2C粉体,会产生组成相为TiC、Ti3SiC2、TiSi2和Ti5Si3的粉体与颗粒产物。添过量Si并不会促进机械合金化反应合成Ti3SiC2。添适量Al可消除硅化物,明显促进反应合成Ti3SiC2。采用3Ti／Si／2C／0．15Al粉体作原料时,颗粒产物中Ti3SiC2含量最高,为92．8wt％;而采用3Ti／Si／2C／0．20Al粉体作原料时,粉体产物中Ti3SiC2含量最高,为61．9wt％。     

石墨配比对钨极氩弧熔敷层TiC增强相含量及分布形态的影响

利用钨极氩弧熔敷预涂在碳钢表面的钛铁和石墨粉末能够在碳钢表面获得性能优异的TiC增强涂层.预涂粉末Ti、C元素配比及含量对增强相的数量、形态和分布方式有重要影响：一方面,随着预涂粉末中含碳量的增加,熔敷层中Fe2Ti有害相降低,但出现了极少量的石墨相;另一方面,熔敷层中原位合成TiC增强相的含量增加,颗粒尺寸也随之增加,TiC颗粒的树枝状分布形态也由细枝状向粗枝状转化.     

Microstructural evolution during self-propagating high-temperature synthesis of Ti-Al system

In order to investigate the microstructural evolution during self-propagating high-temperature synthesis （SHS） of Ti-Al powder mixture with an atomic ratio of Ti： Al=1：1, a combustion front quenching method （CFQM） was used for extinguishing the propagating combustion wave, and the microstructures on the quenched sample were observed with scanning electron microscope （SEM） and analyzed with energy dispersive spectrometry （EDS）. In addition, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction （XRD）. The results showed that the combustion reaction started from melting of the Al particles, and the melting resulted in dissolving of the Ti particles and forming of Al3Ti grains. As the Al liquid was depleted, the combustion reaction proceeded through solid-state diffusion between the solid Al3Ti and the solid Ti. This led to the forming of TiAl and Ti3Al diffusing layers. In addition, the combustion reaction is incomplete besides TiAl, there are a large amount of Ti3Al and TiAl3 and a small amount of Ti in the final product. This incompleteness chiefly results from the using of coarser Ti powder.     

Preparation of TiAl/Ti2AlC Composites with Ti/Al/C Powders by In-situ Hot Pressing

TiAl/Ti2AlC composites were prepared by in-situ hot pressing of TilAl/C powders mixtures and sintered at different temperatures were investigated by X- ray diffraction （ XRD ） of samples. The reaction procedure of Ti-Al-C system could be divided into three stnges. Below 900℃ , Ti reacts with Al to form TiAl intermetallics ; above 900 ℃ , C reacts with remain Ti to form TiC triggered by the exothermal reaction of Ti and Al ; TiAl reacts with TiC to produce dense TiAl/Ti2AlC compasites.In the holding stage, ternary Ti2AlC develops to layered polycrystal and composites pyknosis in the meanwhile. The mechanism of synthesis and microstructure was especially discussed.     

Effect of the addition of Al-Ti-C master alloy on the microstructure and microhardness of a cast Al-10Mg alloy

The microstructure and microhardness of a cast Al-10wt%Mg （henceforth Al-10Mg） alloy with 0.2wt% addition of Al- 5Ti-0.25C master alloy were compared with those of a refiner-free alloy of similar chemical composition. It was found that this level of the master alloy addition not only caused an effective grain refinement, but also caused a significant increase in the microhardness of the Al-10Mg alloy. Microchemical analysis revealed that TiC particles existed in the grain center. The relationship between the holding time and grain size was also studied. It shows that the grain refining efficiency is faded observably with the holding time. This is explained in terms of the instability of TiC particles.     

Study on Grain Refining and Metamorphism of ZL111 Aluminium Alloys

Vacuum sintering and ball milling methods were employed in the preparation process of Ti-C grain refinement and the ability of refiners with varying ratios of Ti and C to refine ZL111 crystal grains was tested. The refinement effect of the Ti-C ratios on tensile strength, elongation percentage, Brinell hardness, pro-eutectoid αAl and the size of the Si phase of ZL111, after modification by rare-earth and strontium nitrate, were studied by means of metallographic examination, SEM and mechanical property tests. The results show that there is an obvious increase in the tensile strength and elongation percentage of refined ZL111 with these new Ti and C refiner compounding powders, while Brinell hardness remained more or less constant. The pro-eutectoid αAl is considerably reduced in size and the Si phase shows a finer and rounder structure. The refiner exhibits a good grain refining performance when the Ti-C ratio is 25：1, for Al crystals can favorably easily form nuclei and grow up along the TiC surface thanks to the TiAl3 generated by surplus Ti and Al. The mechanical properties have clearly been improved by the addition of strontium nitrate to ZL111. The effective factors in the modification of mechanical properties of ZL111 are in order of importance： strontium nitrate, Ti-C ratio and rare earth.     

强磁场下金属熔体中颗粒运动的行为研究

将A1-5Ti-1B中间合金在有无磁场的条件下进行重熔凝固实验,对凝固后的样品金相组织进行了观察．分析了其中未熔化的固相颗粒在组织中的分布和排列状况,结果表明：与不施加磁场时的样品中针状的TiAl3颗粒杂乱无章排列相比,10T强磁场下的样品中呈长轴平行于外场方向排列;同时,重力引起的颗粒沉降行为明显较无磁场时的要弱．说明强磁场对金属熔体中固相颗粒迁移和旋转的行为有重要影响：针状的弱磁性颗粒在形状各向异性的影响下发生了磁致旋转,使之平行于外场排列;而施加强磁场后熔体的表征黏度系数增大抑制了颗粒的沉降行为．因此,可通过改变磁场参数控制凝固组织中强化相的分布和排列,制备性能优良的金属基颗粒复合材料．     

Three dimensional microstructures and wear resistance of Al-Bi immiscible alloys with different grain refiners

The three dimensional(3D) microstructures of Al-Bi alloys with different grain refiners(Al-5Ti-B, Al-3B and Al-3Ti) have been studied using synchrotron X-ray microtomography. The relationships between the microstructures and the corresponding wear behavior are verified through the friction and wear tests. The worn surfaces of the samples with grain refiners tested under 15 and 60 N loads are analyzed using Scanning Electron Microscopy(SEM). The results indicate that the addition of grain refiners is beneficial to the size and distribution of the Bi-rich particles in Al-Bi alloys. Compared with Al-5Ti-B and Al-3B grain refiners, the Bi-rich particles are more uniformly distributed and spherical with finer size with the addition of Al-3Ti grain refiner. The refinement renders the Al-20wt%Bi alloy refined by Al-3Ti the superior wear resistance with respect to those refined by Al-5Ti-B and Al-3B grain refiners, corresponding to the microstructures with fine and uniformly distributed Bi-rich particles in the Al matrix.     

Grain Refining Performance of SHS Al—50TiC Master Alloys for Commercially pure Aluminum

An Al-50wt^TiC composite was directly synthesized by self-propagating high-temperature synthesis(SHS) technology,and then was used as a grain refining master alloy for commercially pure aluminun.The microstructure and grain refining performance of the synthesized master alloy were emphatically investigated.The SHS master alloy only ocntained submicron TiC particles except for Al matrix.Moreover,TiC particles were relatively free of agglomeration.Grain refining tests show that adding only 0.1wt^ of the master alloys to the aluminum melt could transform the sturcture of the solidified samples from coarse columnar grains to fine almost 1.5h at 1003K.Therefore,it is concluded that the SHS master alloy is an effective grain refiner for aluminum and its alloys,and that it is highly resistant to the grain refining fading encountered with most grain refiners.     

Kinetics of Combustion Synthesis in Ti-C-3Ni-Al System

The Kinetics and mechanisms of the combustion reaction in theTi-C-3Ni-Al system were studied. Samples were prepared by igniting compacts of elemental Ti, C, Ni and Al powders with a heating tungsten coil under an inert argon atmosphere. The activation energies of Ti+C+50wt%(3Ni+Al)→TiC+50%Ni3Al and Ti+C+80wt%(3Ni+Al) →TiC+80%Ni3Al exothermic reactions were determined by measuring the combustion wave velocity and the combustion temperature, which are 129kJ.mol-1 and 79kJ*mol-1, respectively. The mechanism of formation of products for Ti-C-3Ni-Al system was found:metal phases (Ti-3Ni-Al) are melted in combustion process,and carbon dissolves into the liquid metal and TiC is subsequently precipitated out of solution, and Ni3Al is crystallized during the cooling process. The mechanism is fairly similar with that of Ti+C→TiC and Ti+C+Ni→TiC+Ni. There are two reactions (Ti+C→TiC, 3Ni+Al→Ni3Al) in the Ti+C+3Ni+Al system, and the wave velocity is mainly controlled by the velocity of Ti + C→TiC, but the velosity of 3Ni+Al→Ni3Al may play a significant role when Ni3Al contents are higher than 70wt%.     

TiA(l)-10Nb合金铸态组织演化规律的研究

研究Ti-(44～54)Al-10Nb合金铸态组织的演化规律,并确定全β凝固的TiAl-10Nb合金的成分范围.实验结果表明:Ti-(44～53)Al-10Nb合金的凝固组织为典型的柱状晶组织,Ti-54Al-10Nb合金的宏观组织为等轴组织;在其凝固组织(纵截面)上部存在较多的缩松,这主要是由于Nb元素的添加量加多,...     

Fabrication and Mechanical Properties of TiC／TiAl Composites

TiC/ TiAl composites with different TiC content were fabricated by rapid heating technique of spark plasma sintering ( SPS ). The effect of TiC purticles on microstructure and mechanical properties of TiAl matrix was imestigated. The results indicate that grain sizes of TiAl matrix decrease and mechanical properties are improved because of the addition of TiC particles. The composites display a 26.8% increase in bending strength when 10wt% TiC is added and 43.8% improvement in fracture toughness when 5ut% TiC is added compared to values of TiC-free materials. Grain-refinement and dispersion-strengthening were the main strengthening mechanism. The improvement of fracture toughness was due to the deflexion of TiC particles to the crack.     

(Ti,Fe)-Al-C体系钢铁基复合材料的热力学计算与分析

利用溶液热力学理论,研究了(Ti,Fe)AlC体系钢铁基复合材料可能的反应产物的吉布斯自由能变化。热力学实验模型是在FeC熔液中加入钛铁合金(Ti,Fe)和纯铝块,继续加热到1600℃,熔液经过充分混合、反应后随炉冷却到常温。计算结果表明,TiC先于Fe2Ti、Fe3C等相生成,但始终没有Al4C3和TiAl3相产生;体系中TiC的热力学稳定性最高;在凝固过程中,TiC相优先析出,随后可能有Fe2Ti、Fe3C等相析出;铝含量的增加能够促进TiC、Fe2Ti、Fe3C等相的生成。     

机械诱发自蔓延反应合成Ti3AlC2的机理研究

以3Ti／Al／2C粉体为原料,采用机械合金化的方法以合成Ti3AlC2材料。研究结果表明,在机械合金化过程中诱发自蔓延反应,反应会产生大量坚硬的小块体颗粒,大小约为0．2-11mm。粉体的组成相为TiC、Ti3AlC2、Ti2AlC,而块体仅含有TiC和Ti3AlC2。获得的粉体和块体产物中Ti3AlC2含量分别约为63wt％和84．8wt％。提出了一个机械诱发自蔓延反应合成Ti3AlC2的反应机制,即Ti3AlC2是从固相TiC与Ti-Al液相中形核并长大。     

Wetting behavior of graphite and CFC composites by Cu-Ti compacts

The wetting behavior of Cu-Ti powder compacts with 22 wt %Ti and 50 wt %Ti on carbon materials, including graphite and carbon fiber reinforced carbon composites(CFC), has been investigated in a vacuum using the sessile drop method. The equilibrium contact angles of Cu-22Ti(containing 22 wt%Ti) on the graphite and the CFC substrates at 1 253 K are 32 o and 26 o, respectively, whereas the equilibrium contact angle of 9° is obtained for Cu-50Ti(containing 50 wt%Ti) on both the graphite and the CFC substrates at 1 303 K.Microstructural analysis of the wetting samples shows that a thin TiC reaction layer is developed at the interfacial area and Ti-Cu intermetallic compounds are formed over the reaction layer. The investigation on the spreading kinetics of Cu-Ti compacts on carbon materials substrates at fixed temperatures reveals that the spreading is controlled by the interfacial reactions in the first stage and then by the diffusion of the active Ti from the drop bulk to the triple line in the later stage. The spreading is promoted by the intense reaction at higher Ti concentrations.