Shipu Chen

Effect of Partitioning Treatment on the Mechanical Property of Fe-0.19C-1.47Mn-1.50Si Steel with Refined Martensitic Microstructure

In order to understand the effect of microstructural features on the mechanical property, quenching and partitioning (Q&P) and quenching and tempering (Q&T) treatments were carried out on a cold-rolled low-carbon Fe-0.19C-1.47Mn-1.50Si steel sheet. It has been shown that because of the rolling in advance, the grain size of prior austenite was dramatically reduced, which resulted in a great decrease in martensite packet/block size and an increase in dislocation density in martensite in the as-quenched state. However, there was no obvious change in average lath size. Different from Q&T treatment, Q&P not only stabilized a large amount of retained austenite, but also led to a serious carbon depletion in martensite as revealed by X-ray diffraction and three-dimensional-atom-probe analyses. In Q&T and Q&P samples, refining martensitic microstructure improves both the strength and impact toughness markedly but does not affect the elongation very much. Compared with Q&T sample, Q&P one is softer due to the existence of considerable amount of retained austenite and less carbon content in martensite, i.e., it has higher elongation and impact toughness but lower strength. Analyses indicated that the strength loss caused by carbon depletion in martensite is critical which has even completely covered up the strengthening effect of microstructural refinement. On the other hand, the carbon depletion in martensite is more essential in improving impact toughness, comparing the role of microstructural refinement and the existence of more retained austenite. Through a combination of rolling and Q&P processes, the refined Q&P microstructure was achieved for a greatly improved product of strength and elongation and a much lower ductile-to-brittle transition temperature.

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.

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.