Gengxiang Hu

Three stage yielding phenomenon in a NiAlFe alloy

The binary NiAl alloy is extremely brittle at ambient temperatures, so it is withdrawn from practical applications as structural materials or shape memory alloys. It has been found that iron is one of the effective elements in improving the ductility of the NiAl alloy. The NiAl-Fe alloys with ([gamma]+[beta]) dual-phase microstructures have good ductility and also good hot-working properties. These results provide the possibility for using the NiAl-Fe alloys for commercial use. However, there are still many experiments to be performed before these alloys can be practically used. The present paper reports a part of the authors work on the deformation behavior of a NiAl-Fe alloy with a ([gamma]+[beta]) microstructure.

The role of hot-working on the microstructure and mechanical properties of the L12-type manganese-modified Al3Ti alloy

Abstract The crystal structure of a manganese-modified Al3Ti intermetallic alloy has been changed from the tetragonal D022 to the L12 cubic structure. The cast alloy shows considerable compression ductility at room temperature. To improve its mechanical properties further, hot-working experiments have been conducted. The results showed that the Al67Mn8Ti25 intermetallic alloy maintains very good hot-workability, the cast alloy can be reduced 60% by a single hot-pressing stroke without cracking. The role of hot-working on the microstructure and the mechanical properties of the alloy have been studied. It was found that the hot-worked alloy shows a deformed structure and some work-hardening after hot-working. Experiments indicated that the starting temperature for recrystallization is about 1173 K and complete recrystallization of the deformed alloy occurs at about 1273 K. Good hot-workability and a high recrystallization temperature permit potential for elevated temperature use. A transmission electron microscopy study on the evolution of dislocation structures in the recovery and recrystallization processes is also reported.

Interface Reaction In Sic Reinforced Al 3 Ti-Based Intermetallic Matrix Composites

The Al 3 Ti-based Ll 2 intermetallic alloy Al 66 Fe 9 Ti 25 has shown low density, high oxidation resistance, good strength and appreciable compression ductility at room temperature. To explore the approach of combined toughening and strengthening of this alloy, composites are being studied. The interface reactions between Al 66 Fe 9 Ti 25 matrix and SiC reinforcement material during different fabrication processes were investigated using SEM, EDS, EPA and X-ray diffraction analyses. The extent of reaction was determined and the reaction products were identified. It was found that SiC is chemically incompatible with the Al 66 Fe 9 Ti 25 matrix, strong interfacial reactions occurred during fabrication and the formation of ternary compounds leads to the deterioration of the matrix alloy.

Investigation of a new type of Al{sub 3}Ti-based L1{sub 2} alloy with second phase precipitation

Since the L1{sub 2} structured Al{sub 3}Ti alloy exists only in a narrow compositional range, further alloying of the single phase L1{sub 2} alloy to improve its property seems hardly successful. Developing two-phase or multiphase Al{sub 3}Ti alloys may be an effective approach for strengthening and toughening. In this article, a new type of Al{sub 3}Ti-based alloy which has a L1{sub 2} matrix with precipitates of a second phase is reported. The quaternary alloys based on Al{sub 67}Mn{sub 8}Ti{sub 25}, and modified with Nb additions, consist of an L1{sub 2} matrix and DO{sub 22} second phase particles in the annealed state, but the second phase can be dissolved by solution treatment and precipitated during high temperature aging. Remarkable strengthening and promising compressive ductility were exhibited by the experimental alloy. The influence of composition on the microstructure and properties of the alloys are reported also.

Effects of boron on the mechanical behaviour of a Ni-rich NiAl alloy

The NiAl based intermetallic alloys are currently of considerable interest as new structural materials because of their relatively low density, comparatively high melting temperature and excellent high temperature oxidation resistance. It has also been found that the Ni-rich (62-65 at % Ni) NiAl alloys with the [beta] (B2) structure undergo a thermoelastic martensitic transformation and exhibit the shape memory effect (SME). Unfortunately, the binary NiAl alloys are extremely brittle at ambient temperature and, therefore, are restricted in practical application. The micro-alloying and macro-alloying methods are commonly used to overcome the brittleness of the alloys. It is reported that boron is the most effective microalloying element in improving the ductility and suppressing the intergranular fracture of the Ni[sub 3]Al intermetallic compound containing aluminium less than 25 at %. However, whether boron has a beneficial effect on the binary NiAl alloy with the B2 structure is not clear. The present paper reports the effect of boron on the mechanical 1 and martensitic transformation in a NiAl alloy containing 37.5 at % Al with the B2 structure.

TEM and computer image simulation studies on the dissociation of superdislocations in L1{sub 2} Al{sub 3}Ti alloy

TEM investigation associated with computer image simulations were conducted to determine the dislocation core structure in the L1{sub 2} Al{sub 67}Mn{sub 8}Ti{sub 25} alloy deformed at room temperature. It is identified that the a{l_angle}110{r_angle} superdislocations dissociated into pairs of a/3{l_angle}112{r_angle} superpartials with SISF between them. The theoretical and experimental micrographs are in good agreement under various diffraction conditions. The unusual temperature dependence of flow stress at low temperature can be related to the SISF-type dissociation.