Ti Al Powder Mixture Research Articles

Self-combustion of Ti-C and Ti-Al Powder Mixture in a Nitrogen Atmosphere: Product Application as Reinforcement in Metal Matrix Composites

In this work, two copper metal matrix composites (MMCs) reinforced with 20 wt.% of Ti(C,N) or Ti2AlN particles were studied. The reinforcement particles were synthesized by flash sintering under 2 bar nitrogen atmosphere causing an SHS reaction ignited by electrical current. This reaction led to produce TiC0.7N0.3 solid solution for the MMC1 reinforcement and Ti2AlN, TiN, and Ti3Al titanium aluminide for the MMC2 reinforcement. Both MMCs were densified by liquid phase sintering. The structural characterization was performed by XRD analysis while the morphology and chemical element distribution of both MMCs were analyzed by SEM and EDS. The structure of the two MMCs was relatively dense and showed good wettability. The mechanical and tribological behavior of MMCs evaluated by nanoindentation and wear testing reveals that the addition of 20 wt.% of reinforcement considerably improves the properties of copper matrix. Indeed, the MMC1 proved to be 3 times harder and 10 times more wear-resistant than the MMC2 composite.

Structural state of the Ti–Al powder mixture at various stages of mechanoactivation treatment

Structural state of the Ti–Al powder mixture at various stages of mechanoactivation treatment

Low-weight TiAl3 composites by thermal explosion

Dispersion-strengthened TiAl3-based material with uniform structure and high compression strength (σc ≈ 850 MPa) was SHS-produced from Ti–Al–B4C blends in a mode of thermal explosion by using the B4C particles coated with a TiB2/TiC layer as a strengthening agent and preliminary mechanical activation of Ti–Al powder mixtures. The Ti + 3Al mixtures were mechanically activated in a planetary mill for 3 or 6 min and then 10 or 20 wt % of coated B4C particles were added. Pelleted samples were placed into a reaction chamber and heated in an electric furnace under Ar to a self-ignition temperature. The process was optimized and recommended for practical implementation.

Multiscale composition modulated Ti–Al composite processed by severe plastic deformation

Using severe plastic deformation processes to consolidate and co-deform powder mixtures to make ultrafine grain composites is a very attractive approach because it offers an almost non-limited room for combinations of phases and composite structures. The aim of this work was to investigate the mechanisms operating at different length scales and leading to multiscale structures, namely co-deformation, fragmentation and mechanical mixing. A Ti–Al composite was processed from a Ti–Al powder mixture prepared by ball milling and subsequently deformed by equal channel angular pressing. Microstructures were characterized at all length scales, down to the nanometre, using optical microscopy, scanning electron microscopy and transmission electron microscopy. It was found that the final structure exhibits unique features at various length scales. Chemical heterogeneities at the micron scale are the result of co-deformation, while at the sub-micron scale they result from the fragmentation and necking of the Ti hard phase. Then, at the nanometer scale, intermixing occurred and nanoscaled intermetallic particles were discovered. This work highlights the possibilities offered by all these mechanisms to design ultrafine grain composite structures for optimized properties.

Combustion synthesis of TiAl intermetallics and their simultaneous joining to carbon/carbon composites

The combustion synthesis of TiAl intermetallics and their joining to carbon/carbon composites was realized simultaneously. The successful joint configuration involved putting a carbon/carbon composite ball into the Ti–Al powder mixtures. The effect of the residual stresses at the interface on the joining of carbon/carbon composite to TiAl intermetallics was analyzed. Investigation of the reaction products of Ti–45 at.% Al mixtures showed that TiAl and Ti3Al phases were formed by combustion synthesis. The evolution of the interfacial microstructure was investigated.

1506 スポット溶接機によるTi-A1混合粉末の通電焼結(機械材料・材料加工I)

1506 スポット溶接機によるTi-A1混合粉末の通電焼結(機械材料・材料加工I)

Formation of TiAl–Ti 2AlC in situ composites by combustion synthesis

Preparation of TiAl–Ti 2AlC in situ composites with a broad range of composition was conducted by self-propagating high-temperature synthesis (SHS) with compressed samples from the mixture of elemental powders. When compared with SHS formation of monolithic TiAl, the addition of carbon particles to the Ti–Al powder mixture enhances the sustainability of the reaction. It was found that no prior heating was required for the samples prepared to produce the composites containing more than 20 mol% Ti 2AlC, in contrast to the need of preheating at 200 °C for single-phase TiAl formation. This is attributed to the fact that formation of Ti 2AlC is more exothermic than that of TiAl. As a result, the combustion temperature and combustion wave velocity increase with the content of Ti 2AlC formed in the TiAl–Ti 2AlC composite, and approach the values associated with formation of single-phase Ti 2AlC when considerable amounts of Ti 2AlC are yielded. The XRD analysis of the end products confirms formation of TiAl–Ti 2AlC in situ composites. Moreover, simultaneous formation of Ti 2AlC promotes the phase evolution of the aluminide compounds. That is, the secondary aluminide phase, Ti 3Al, was no longer detected in the TiAl–matrix composites containing Ti 2AlC of 30 mol% or above.

Nitride formation during combustion of Ti-TiO2 and Ti-Al powder mixtures in air under SHS conditions

Nitride formation during SHS combustion of a micron-size titanium powder and its mixtures with additives in air was studied. It was shown that the yield of TiN Ti powder was higher for SHS combustion in air than for SHS combustion of powders of the same degree of dispersion in nitrogen. The mechanism of formation of TiN is probably determined by the reaction of the intermediate product TiO with atmospheric nitrogen.

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.

Formation of TiAl–Ti 5Si 3 and TiAl–Al 2O 3 in situ composites by combustion synthesis

Preparation of TiAl–Ti 5Si 3 and TiAl–Al 2O 3 in situ composites with a broad range of composition was conducted by self-propagating high-temperature synthesis (SHS). Sample compacts containing Ti, Al, and TiO 2 powders were employed to produce the TiAl–matrix composite reinforced by Al 2O 3, which was yielded through the displacement reaction of Al with TiO 2. On the other hand, elemental powder compacts were used to synthesize the TiAl–matrix composite with Ti 5Si 3 as the reinforcement. Experimental observations show that the addition of Si in the Ti–Al powder mixture enhances the sustainability of the reaction and the increase of Ti 5Si 3 formed in the composite increases the combustion temperature and combustion wave velocity. However, the opposite trends were found in the synthesis of TiAl–Al 2O 3 composites. Not only is a preheating temperature of 300 °C required to achieve self-sustaining combustion, but also the reaction temperature and flame-front propagation rate decrease with Al 2O 3 content. Moreover, it was found that the combustion front propagated in a pulsating mode when the mole fraction of Al 2O 3 higher than 12.5 mol% was produced, because of the lower exothermicity of the reaction between Al and TiO 2 than that of Ti with Al. The Al 2O 3 content of the TiAl–Al 2O 3 composite obtained by this study has an upper limit at 28.6 mol%, beyond which combustion ceased to propagate. The XRD analysis of the end products confirms formation of TiAl–Ti 5Si 3 and TiAl–Al 2O 3 in situ composites. In addition to TiAl, another aluminide compound Ti 3Al known as a major secondary phase in the Ti–Al reaction was detected in both types of the composites.

Al–FeAl–TiAl–Al 2O 3 composite with hybrid reinforcement

The process of obtaining cast aluminium composite of dispersive structure and hybrid reinforcement has been presented in the article. An Aluminium alloy (AlMg 2) was modified with a powder mixture which, when in reaction with aluminium, reinforced the matrix with intermetallic phases and aluminium oxide. According to the technological conception, an assumption was made, that the cast composites would be produced in technological procedure shown in Fig. 1. The reinforcing phases were using Fe–Ti–Al powder mixtures with aluminium oxide formed in a self-propagating high-temperature synthesis (SHS). The structure and phase composition of the composite powder used for the matrix alloy modification are shown in Fig. 2. A composite alloy Al–FeAl–TiAl–Al 2O 3 was produced by casting method (gravity casting, mechanical mixing) after which its structure was determined. It was assumed that the final product of the applied production process will be an aluminium composite with hybrid reinforcement, consisting of Fe–Al and Ti–Al intermetallic phases and aluminium oxides. Optical microscopy, electron scanning microscopy and X-ray phase analysis were used to characterize the microstructure of the composites produced. Presence of aluminium, Al 3Ti and Al 13Fe 4 phases and dispersed Al 2O 3 was confirmed in the composite by XRD method. The dispersion structure and phase composition of the composites are presented in Figs. 3–6. The composites formed in an in situ reaction constitute a newer generation of casts, in which dispersion reinforcement is obtained in the form of intermetallic and ceramic phases coherent with the matrix, very often below 1 μm in size. The designed process allows for the structure modification of the applied casting aluminium alloys in different technological variants.

金属間化合物の粉末冶金と諸物性 窒素ショックＭＡとパルス通電加圧焼結により合成したＴｉＡｌ−ＴｉＢ２複合材料の特性に及ぼす窒素の影響

The authors formerly found out that intercurrent introduction of gas into the milling atmosphere during mechanical alloying of Ti-Al powder mixture promotes the synthesis of alloy powder and named this process nitrogen shock mechanical alloying. It was confirmed by x-ray diffraction analysis that nitride, Ti2AIN was formed in sintered bodies of the alloy powder synthesized by the shock MA. It is expected that TiAl matrix can be strengthened by the nitride, if the nitride precipitates in the form of fine particles dispersed in the matrix.In this study, the shock MA was applied to a mixture of Ti, Al and B powders to make a Ti-Al-B alloy powder and the alloy powder was consolidated by spark plasma activated sintering, in order to investigate effects of on the microstructure and properties of sintered bodies. Boron was added in expectation of the formation of fine TiB2 particles which strengthen the matrix as well as the nitride. As a result, it was found that taken in the alloy powder enhances amorphization of the powder. It was also found that the nitride increases hardness and Young's modulus of the sintered bodies. However, the nitride formed excessively made the microstructure of the sintered bodies uneven.

Mechanistic processes influencing shock chemistry in powder mixtures of the Ti-Si, Ti-Al, and Ti-B systems

Shock-recovery experiments were performed on Ti-Si, Ti-Al, and Ti-B powder mixtures to produce compacts of reacted and unreacted states to characterize the reaction product microstructure as well as the shock-compressed configuration of unreacted constituents. Microstructural and X-ray diffrac-tion (XRD) peak broadening analyses were performed on unreacted compacts to determine the con-figurational changes occurring during shock compression of powders and to quantify the differences in the deformation response of the reactants in each system. The results of the present work dem-onstrate that the mechanistic processes leading to shock-induced reactions are dominated bydiffer-ences in the shock-compression response of the powder mixture reactants. It was established that the propensity for initiation of shock-induced chemical reaction decreases from Ti-Si to Ti-B to Ti-Al powder mixtures, irrespective of the differences in the thermodynamic characteristics of these sys-tems. The differences in the mechanical properties of the reactants influence the shock-compression response (deformation or fracture and flow behavior) and mixing of reactants, and therefore, the configuration changes prior to initiation of shock-induced chemical reactions.

Mechanical Alloying of Ti–Al Powder Mixtures under Nitrogen Atmosphere

Elemental titanium powder and Ti100−xAlx elemental powder mixtures were milled in a vibrational ball mill, Spex 8000, under nitrogen atmosphere, and the nitrogen absorption behavior during milling and the structures of milled powders were examined by means of X-ray diffraction measurements, SEM and HRTEM observations. The titanium powder absorbed 50 at% of nitrogen during milling and was nitrided completely to form TiN. The Ti–Al powder mixtures with compositions X≤50 absorbed also about 50 at% of nitrogen and were nitrided completely to form a solid solution nitride (Ti, Al)N with the NaCl-type structure through an amorphous-like solid solution. Each of the TiN and (Ti, Al)N powder particles had a nanocrystalline structure consisting of about 5 nm size grains. In the case of the Ti100−xAlx powder mixtures with compositions 60≤X≤70, 35-15 at% of nitrogen were absorbed in the powders and each of the milled powders had a dual-phase structure consisting of about 5 nm size (Ti, Al)N and Al–Ti solid solution phases. The Ti–Al powder mixtures with compositions 80≤X≤100 scarcely absorbed nitrogen and therefore no nitrides formed. The main reason why the aluminum rich Al–Ti powder mixtures scarecely absorb nitrogen may be ascribed to the fact that aluminum powder is too soft to be-refined by milling.

振動ボールミリングによるＴｉ‐Ａｌのメカニカルアロイング過程におけるミリング粉末粒子の形態と物性の変化

Mechanical alloying process of Ti-Al powder mixtures during vibratory milling was investigated by optical microscopy, SEM, X-ray diffraction analysis, XMA and micro-hardness measurement.Microstructures and phases of HIPed compacts of the milled powders were also investigated. As a result it was found that the amorphization behavior and morphology of the powder particles during milling were strongly dependent on the milling ball size. The phases and the microstructures of the HIPed compacts were affected by the starting powder composition.