The ductility and strength of Fe−Cr−Al alloys

Metal Science and Heat Treatment -     

Properties and heat treatment of Ti−Nb and Ti−Nb−Al alloys

Metal Science and Heat Treatment -     

Inelastic effects in ordering of Fe−Al alloys

The effects of the aluminum content in binary b.c.c. alloys of the Fe−Al system and of the processes of ordering in the substitutional solid solution on the activation energy of diffusion of carbon atoms and magnitomechanical dissipation of the energy of mechanical vibrations are studied. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 3–9, April, 1998.     

Solidification structures of Ti–Al–Cr alloys

Phase transformations in the ternary Ti–Al–Cr alloy system have been studied by combining preliminary phase equilibria calculations and microstructural studies of a number of model alloys. The results have contributed to a better understanding of phase equilibria in the Ti–Al–Cr alloy system above 1273 K. A liquid surface projection has been tentatively proposed. Micro-twins have been observed in the monolithic γ phase within a B2 matrix. This supports a previously proposed mechanism for the formation of such a structure in a B2 matrix. The results also suggest that there is no representative orientation relationship between γ and the Ti(Cr,Al)₂ Laves phase. The L1₂ τ phase can be in direct equilibrium with the liquid phase. The ω phase stability has also been studied. The stability of the ω phase is attributed to the electron density of the prior B2 phase. This leads to changes in the effective heat of formation of the ω structure, as concluded from total energy LMTO calculations.     

On the physicochemical mechanism of modification of Al−Si alloys

Conclusions  

Solidification microstructures and carbides morphology in rapidly solidified Fe−Al−Cr−C alloys

The combined effects of alloying additions and heat treatment on the evolution and development of the microstructures of Fe₃Al-based Fe−Al−Cr−C alloys produced by melt suction processing have been examined. Particular emphasis has been placed on the distribution and morphology of carbides in rapidly solidified Fe₃Al-based intermetallics. The results suggest that the formation of intrinsically hard and brittle Fe₃AlC and Cr₇C₃ type carbides depends on the alloying content. These carbides tend to form preferentially along the grain boundaries where more continuous and coarse networks are observed, especially for alloys having higher Cr and C content. These networks are fragmented as a result of heat treatment at 1200 °C and subsequent air cooling and quenching.     

Phase transformation behavior and shape memory characteristics of Ti−Ni−Si alloys

Transformation behavior, microstructures and shape memory characteristics of Ti−(50−X)Ni−XSi (X=2, 4, 6 at.%) and (50−X)Ti−Ni−XSi (X=2, 5, 7, 10 at.%) alloys were investigated by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, electrical resistivity measurements and constant load thermal cycling tests. Ti₅Si₃, Ni₁₆Ti₆Si₇ and Ni₄Ti₄Si₇ were formed in Ti−(50−X)Ni−XSi alloys, while Ti₅Si₄, Ni₃Si, Ni₃Ti₂ and Ni₃Ti₂Si were found in (50−X)Ti−Ni−XSi alloys. The total amount of silicides increased with increasing Si content, irrespective of Si content. The B2→B19 transformation occurred in Ti−(50−X)Ni−XSi alloys, and their transformation temperatures appeared to be almost constant. Transformation elongation associated with the B2→B19 transformation decreased with increasing Si content. In contrast to Ti−(50−X)Ni−XSi alloys, a transformation accompanied with structural change did not occur in (50−X)Ti−Ni−XSi alloys.     

Indirect evaluation of the long-term oxidation properties of Al−21Ti−23Cr and Al−37Ti−12Cr coating materials for TiAl alloy

The most pertinent coating materials in the Al−Ti−Cr alloy system to improve the high temperature oxidation resistance of a TiAl alloy, with respect to oxidation properties, resistance to thermal stress, and chemical compatibility, are the two-phase alloys of Al−21Ti−23Cr (L1₂+Cr₂Al) and Al−37Ti−12Cr (γ+TiAlCr). In this study, cyclic oxidation tests at 1000 °C and 1200 °C were performed for the specimens coated with both materials of 10 im thickness. Furthermore, breakaway oxidation caused by the formation of a rutile TiO₂ scale was observed, though both bulk alloys showed very stable oxidation behavior. This phenomenon was resulted from the depleted Al content in the coating layer due to Al₂O₃ oxide growth and interdiffusion with the substrate. Considering the decrease of Al content due to oxide growth, the Al−21Ti−23Cr coating with the initial higher Al content was more effective for long-term oxidation protection of the TiAl alloy. On the other hand, when the Al content changes due to the interdiffusion with the substrate, the Al−37Ti−12Cr coating with a smaller compositional gradient with the TiAl substrate was more effective than the Al−21Ti−23Cr coating. Cyclic oxidation tests at 1000 °C and 1200 °C confirmed that for the longer lifetime of coating materials the initial Al content was more important than the smaller compositional gradient with the substrate. Consequently, the Al−21Ti−23Cr coating was considered as more effective one for the long-term oxidation resistance of TiAl alloys.     

Hydrogen absorption and desorption in Ti−Al alloys

Binary Ti_1−xAl_x and ternary Ti_0.75−xAl_0.25M_x (M=V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Pd, Hf, Ta and W; x=0.15 and 0.25) alloys reacted slowly with 5.0 MPa H₂ at room temperature for different periods. The hydrogen absorption capacity, the 50% hydrogen desorption temperature (T _d) and the structures of their hydride were investigated. Amorphous and fcc type hydrides formed by hydrogenation of the binary Ti−Al alloys. As the Al concentration increased in the Ti−Al alloys, the hydrogen absorption capacity decreased, while the hydrogen desorption temperature decreased at once and then increased again. Amorphous, fcc, bcc and C14 Laves type hydrides formed by hydrogenation of the ternary Ti₃Al− based alloys. The hydrogen absorption capacity was reduced despite whatever elements were substituted for Ti in Ti₃Al. Ni, Co, Mn and Nb have the ability to reduceT _d of Ti_0.75−xAl_0.25M_x. This article based on a presentation made in the symposium “The 2nd KIM-JIM Joint Symposium: Hydrogen Absorbing Materials”, held at Hanyang University, Seoul, Korea, October 27–28, 2000 under the auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Thermal stability of nanocrystalline Al−10Fe−5Cr bulk alloy

Thermal stability of nanocrystalline Al?10wt.%Fe?5wt.%Cr bulk alloy was investigated. The initial micro-grained mixture of powders was processed for 100 h using mechanical alloying (MA) to produce nano-grained alloy. The processed powders were sintered using high frequency induction heat sintering (HFIHS). The microstructures of the processed alloy in the form of powders and bulk samples were investigated using XRD, FESEM and HRTEM. Microhardness and compression tests were conducted on the bulk samples for evaluating their mechanical properties. To evaluate the thermal stability of the bulk samples, they were experimented at 573, 623, 673 and 723 K under compression load at strain rates of 1×10^?1 and 1×10^?2 s^?1. The annealed samples exhibited a significant increase in their microhardness value of 2.65 GPa when being annealed at 723 K, as compared to 2.25 GPa of the as-sintered alloy. The bulk alloy revealed compressive strengths of 520 MPa and 450 MPa at 300 K and 723 K, respectively, when applying a strain rate of 1×10^?1 s^?1. The microstructural stability of the bulk alloy was ascribed to the formation of iron and chromium containing phases with Al such as Al₆Fe, Al₁₃Fe₄ and Al₁₃Cr₂, in addition to the supersaturated solid solution (SSSS) of Cr and Fe in Al matrix.     

Ti−V−Cr BCC alloys system with high protium content

This paper aims to study the relationship between the protium absorption properties and alloy composition of Ti−V−Cr alloys. We studied the effects of composition of the alloys and the heat-treatment on the protium absorption-desorption properties of Ti−V−Cr alloys, and found that Ti−35V−40Cr alloys show 2.6 mass% protium capacity. The plateau pressure of the alloys increased with decreasing lattice constants, resulting from increasing Cr content. The main phase of the samples containing more than 15%V was a BCC phase in the cast state. These BCC phase alloys exhibited 2.4 mass% protium. It was also found that the heat-treatment was effective in stabilizing a BCC structure in Ti−V−Cr alloys with low V content. The alloy yields the high capacity of 3.0 mass% protium capacity, which will be the highest value at 313 K reported so far. The alloy will be promising since it contains a low amount of the expensive V element. This article based on a presentation made in the symposium “The 2nd KIM-JIM Joint Symposium: Hydrogen Absorbing Materials”, held at Hanyang University, Seoul, Korea, October 27–28 under the auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

The influence of Cr alloying on microstructures of Fe–Al–Mn–Cr alloys

The effects of increasing chromium content on the phase transformations in Fe–Al–Mn–Cr alloys have been investigated by means of transmission electron microscopy and energy-dispersive X-ray spectrometry. The experimental results revealed that increasing the chromium addition would expand both the A12α-Mn and DO₃ phase-field regions.