Microstructural analysis of titanium aluminide formed in situ in an aluminium matrix composite (original) (raw)
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The evolution of titanium powders in the pure aluminum melt at a lower temperature was studied in our research. The process involved some titanium powders being added into the pure aluminum melt at 1003 K (730°C), and then the melt was cast into an ingot after 5 minutes. A reaction layer composed of some loose Al 3 Ti particles was formed on the solid Ti surface due to the reactive diffusion between titanium and aluminum. In-situ blocky Al 3 Ti particles smaller than 5 lm were produced in the aluminum matrix. A reaction-peeling model was suggested to illustrate the formation mechanism of Al 3 Ti particles, and a simple approach for fabricating in-situ Al 3 Ti/Al-alloy composites was proposed as well.
Thermal and X-ray analyses of aluminum–titanium nanocomposite powder
Journal of Thermal Analysis and Calorimetry, 2017
The present study has investigated the complex mechanisms in the aluminum-titanium system with different percentages of titanium through a combination of thermal and X-ray analyses. Thermogravimetry, derivative thermogravimetric, X-ray diffraction, scanning electron microscope and transition electron microscope were used for characterization of the samples. Initially, different Al-Ti powder mixtures were produced by high-energy ball milling and after 30 h of milling the phases generated at different percentages of Ti were analyzed. The XRD results revealed that the intermetallic Al 3 Ti powder is obtained after a certain duration of milling. In addition, L1 2 to D0 23 phase transformation is possible with increase of the Ti percent. Analyses of the powder annealed at different temperatures yielded interesting results, including the effect of stearic acid as the surface control agent on phase transformations of the aluminum-titanium system and also the formation of unexpected phases such as Al 4 C 3 and TiC. Moreover, ductile to brittle transition during phase transformations of the intermetallic Al 3 Ti powder was quite conspicuous, which could result in more homogeneity of the powders and the occurrence of more reactions in the system. For example, formation of D0 23-Al 3 Ti powder which is more brittle compared to L1 2 resulted in the exit of Al from among its layers, leading to the increase of the chances for Al reaction with the system impurities.
Journal of Engineering, 2020
The effect of different Ti additions on the microstructure of Al-Ti alloy prepared by powder metallurgy was investigated. A certain amount of Ti (10wt%, 15wt%, and 20wt%) were added to aluminium and the tests like microhardness, density, scanning electron microscope (SEM), optical microscope (OM) and X-Ray Diffraction (XRD) were conducted to determine the influence of different Ti additives on the Al-Ti alloy properties and microstructure. The results show that the grains of α-Al changed from large grains to roughly spherical and then to small rounded grains with increasing Ti content, the micro-hardness of the alloy increases with increasing Ti, and XRD results confirm the formation of TiAl3 intermetallic compound during sintering.
The self-propagating high temperature synthesis of titanium aluminides: A parametric study
The present work reports experimental studies on self-propagating high-temperature synthesis of titanium aluminides. Powder mixture of different Ti:Al atomic ratios were adopted and pressed to make compacts. The compacts were heated up to the ignition temperature from one end using induction heating, giving rise to self-sustaining reaction along the compacts. The propagation of reaction front was monitored using a color CCD camera. X-ray Diffraction analyses showed that the main products constituents were TiAl, Ti 3 Al and TiAl 3 in the case of Ti:Al atomic ratios of 1:1, 3:1, and 1:3, respectively; rapid preheating to temperatures close to ignition temperature resulted in minimization of the occurrence of undesired phases. The effects of various parameters such as the green compact density and titanium particle size on the ignition time, combustion wave velocity, and combustion temperature were studied.
Microstructures of titanium-aluminides produced by laser surface alloying
Journal of Materials Science, 1992
The microstructures of Ti-AI layers (from 43-80 at %AI) produced by laser surface alloying of titanium substrate with a powder feed technique have been investigated. The laser processing parameters were; 1.8 kW laser power, 3 mm beam diameter, 7 mm s-a traverse speed, and values of powder flow rates of aluminium ranging from 0.07-0.11 gs -~. The microstructures were dendrites of 0~ 2 and interdendritic regions of 0~ 2 + y in the Ti-43 at%AI alloy; dendrites of either 0~ 2 or 0~ 2 + y with interdendritic y in the Ti-50 at%AI alloy; dendrites of ~2 + Y with interdendritic y in the Ti-55 at%AI alloy; single phase y in the Ti-60 at%AI alloy and TiAI 3 dendrites and AI solid solution in the interdendritic regions in the Ti-80 at%AI alloy. The microstructures were fine and comparable to those produced by other methods of rapid solidification processing. The microstructures of the Ti-50 and Ti-55 at%AI alloys were in agreement with the existence of the peritectic reactions: L + [3-* ~ and L + 0~7, in the Ti-AI system.
Nanostructured titanium aluminides
Materials Science and Engineering: A, 1994
Binary Ti-A1 and ternary Ti-Al-Nb alloys were mechanically alloyed in a Szegvari attritor or in a SPEX mill, to produce an amorphous phase and a B2/b.c.c. phase respectively. Consolidation of these powders by hot pressing, explosive compaction or hot isostatic pressing resulted in transformation of the as-milled phases; however, the product had retained nanometer-sized grains. The microhardness of the consolidated compacts is about 1000 kg mm-2 and clearly demonstrates that the Hall-Petch equation is applicable.
Al-Al 3 Ti nanocomposite produced in situ by two-step hot-press sintering
IOP Conference Series: Materials Science and Engineering, 2012
Aluminum reinforced with a large amount (up to about 55 vol.%) of Al 3 Ti particles can be fabricated from Al-20Ti elemental nanometer-sized powder mixture via in-situ two step hot press sintering (TSS). For production of intermetallic reinforced in-situ composite, TSS can provide elevated temperature to facilitate the formation of intermetallic phase in situ and hot consolidation to form a fully dense solid. The first step sintering was employed at a higher temperature to obtain an initial high density, and the second step was held at a lower temperature by isothermal sintering for more time than the first one to increase bulk density without significant grain growth. The optimum TSS regime consisted of heating at 625°C for 5 min (1st step) and 570°C for 40 min (2 nd step) with applied pressure of 470 MPa, resulting in the formation of near full dense microstructure (0.97 TD) with suppressed grain growth.
Self-Propagating Synthesis of Ti-Al-C Powder Mixtures
Key Engineering Materials, 2012
Self-propagating synthesis of Ti-Al-C powder mixture was used for fabrication of master alloys suited to industrial scale manufacturing of Al-TiC composites. The cold compacted powder pellets were heated in a protective atmosphere until the melting point of aluminium. Then the temperature of pellets increased rapidly due to intense exothermic reaction between molten Al and Ti, resulting in simultaneous formation of Al 3 Ti and Al 4 C 3. When the temperature exceeded ~1090°C, TiC particles started to form as a result of the mutual reaction between Al 3 Ti and Al 4 C 3. Resulting reaction products consisted of fine (~2µm) TiC particles uniformly distributed in the Al matrix. The composition of powder mixture was optimized to attain master alloy pellets containing ~50 vol.% TiC. Such pellets were then diluted in molten aluminium to produce Al+TiC composites. In-situ formation of TiC in Al matrix provided favourable interfacial quality, which avoided dewetting and rejection of particles from molten aluminium. The parameters for composite casting were optimized in order to reduce the effect of reversible reaction leading to undesired formation of Al 3 Ti or Al 4 C 3. The final composites showed significantly increased Young's modulus and strengths. The potential of using the approach for the fabrication of fine, nearly spherical TiC particulate reinforced Ti composites is briefly discussed. The simple process is very promising for economical manufacturing of highly efficient lightweight structural materials.
As a promising reinforcement of aluminum alloy, in situ formed Al 3 Ti particles have attracted more attention in the fabrication of aluminum matrix composites. In our research, in situ Al 3 Ti/7075 alloy composites were fabricated by adding K 2 TiF 6 salt powders into molten 7075 alloy at 750°C via casting method. The formation of in situ Al 3 Ti particles and their effects on the microstructure and mechanical properties of 7075 alloy, including hardness, ultimate tensile strength (UTS), and yield strength (YS), were investigated. The results showed that in situ formed Al 3 Ti particles were rod-like in morphology, with the average length and width of 15 lm and 5 lm, respectively. Due to the nucleating effect of Al 3 Ti particles, a-Al crystals of 7075 alloy transferred from dendritic to equiaxed structure in morphology, the size of which decreased obviously as well. Compared with 7075 alloy, the hardness, UTS, and YS of in situ Al 3 Ti/7075 alloy were improved by 14.3%, 18.1%, and 25.8%, respectively.
Production, Characteristics, and Commercialization of Titanium Aluminides
ISIJ International, 1991
The production, characteristics, and commercialization of monolithic and composite titanium aluminides are presented with emphasis on use in the demanding aerospace industry. Theelevated temperature properties combinedwith a low density are attractive, but inherently low "forgiveness", and environmental concerns, must be overcome before widespread use will occur,