C.X. Shi

IMPROVEMENT OF SHAPE-MEMORY EFFECT IN FE-MN-SI ALLOY BY CR AND NI ADDITION

It has been reported that Fe-Mn-Si alloys containing 28-34wt%Mn and 4-6.5wt%Si exhibit a good shape memory behavior with the {gamma}{r_arrow}{epsilon} martensite transformation, when the shape deformation is applied at room temperature. Although the theoretical shear for fcc{r_arrow}hcp transformation implies a possible recoverable shape of 20%, usually in Fe-Mn-Si polycrystalline alloy it is limited to about 2%. The poor corrosion resistance and small shape memory effect (SME) in these alloys are two critical problems for their practical applications. In the present study, Fe-20.0Mn-5.1Si-8.1Cr-4.7Ni (wt%) alloy, which has better SME according to the results reported by Otsuka, is chosen to understand the mechanism of improvement of SME in Fe-Mn-Si alloy by addition of Cr and Ni.

Improvement of shape memory effect in an Fe-Mn-Si-Cr-Ni alloy

The shape memory effect (SME) in Fe-Mn-Si based alloys results from the {gamma} {yields} {var_epsilon} transformation and its reverse transformation on heating, however, intersection of {var_epsilon} variants is detrimental to the improvement of the SME in these alloys. In the present study, improvement of SME in Fe-Mn-Si-Cr-Ni alloy by ausforming was investigated and the mechanism for the improvement of SME was proposed according to an analysis of the microstructure.

Corrosion wear of duplex stainless steels in sulfuric acid solution containing chloride

Abstract The corrosion rate, wear rate, corrosion wear rate, variation of Vickers hardness of the worn surface, and the recovery time of passive film were determined for α + γ duplex stainless steel (DSS) in sulfuric acid (H2SO4) or H2SO4 + sodium chloride (NaCl) solution. In the chloride (Cl−) solution, the wear-induced corrosion and the corrosion-induced wear were ∼ 4% and 70% of the total damage, respectively. Damage was less in the absence of Cl−. Morphologies of tracks and debris also were observed. Results showed Cl− embrittled the worn surface of the metal.

THE SOLIDIFICATION BEHAVIOR OF 8090 AL-LI ALLOY

In this work, the solidification and segregation behaviors of 8090 Al-Li alloy have been investigated with differential thermal analysis (DTA) and the metallographic-electron microprobe method. The results show that 8090 Al-Li alloy has a much more complex solidification path than Al-Li binary alloy due to the addition of many alloying elements and the presence of impure elements. Solidification begins at about 635 °C with the reaction of L → α-Al + L′, and this reaction goes on to termination. The alloying element Cu and impure elements Fe and Si have a strong segregation tendency. During solidification, Cu segregates to the interdendrite and finally forms α-Al + T2 eutectic. As a result, the solidification temperature range is greatly extended. Iron and Si form the insoluble constituents Al7Cu2Fe, AlLiSi,etc., although their concentrations in the alloy are quite low. With the increase of Fe content, there is a eutectic reaction of α-Al/Al3Fe at about 595 °C. The formation of insoluble constituents is influenced by both concentrations of impure elements in the alloy and the cooling rate.

The formation and growth of PFZ at grain boundary in Al-11.9at.-%Li alloy

Abstract TEM observations of PFZ formation and growth in Al-11.9at.-%Li at 463K indicates that they are closely related to aging time, which depends on the long-range diffusion of lithium atoms. The particle size of the δ′ phase becomes smaller near the PFZ interface, and thereafter, it consists of lithium-rich supersaturated solid solution in the PFZs. The δ precipitates are nucleated in the grain boundaries when the lithium content is sufficiently high. The half-width of PFZ varies with the square root of aging time, and it can be calculated by the equation w = Kt 1 2 [ K =2 D 1 2 ( C − C ∝ )/( Cx − C ∝ )] in the binary AlLi alloys.

IMPROVEMENT OF SHAPE-MEMORY EFFECT IN AN FE-MN-SI ALLOY BY PRESTRAINING OF AUSTENITE

Abstract The effect of 3% prestraining of austenite on the improvement of SME in Fe-29.9Mn-6.0Si was investigated, over the temperature range 573–1073 K. It was found that by this treatment, the critical stress for the formation of e-martensite decreased and a 3.8% recovery strain and a 2.2% perfect recovery strain could be reached in this alloy.

Effect of P (Mn) content on the coarsening of γ′ in Incoloy 903

Abstract The coarsening of γ′ precipitate in Fe-Ni-Co based alloys with different contents of P (Mn) was investigated by TEM. For both experimental alloys, the growth kinetics of γ′ particles were in good accordance with the prediction of the Lifshitz-Wagner theory of diffusion-controlled coarsening with the exception of a little larger cut off value in the histograms of the γ′ precipitate. Compared with the usual alloy, the alloy with a lower content of P (Mn) showed that the γ′ particles exhibited a lower growth rate, and the density and size distribution of the precipitate were found to be more homogeneous.

Investigation of micro-segregation in Incoloy 903

The effect of P content on micro-segregation in Incoloy 903 alloy was investigated by using electron microprobe analysis and TEM/EDS. It was found that by lowering the P (Mn) content in the alloy, the equilibrium partition coefficients of Nb and Ti increased, solidification micro-segregation of Nb and Ti lowered and formation of the Laves phase was eliminated.

Effect of boron and zirconium on directional solidification behaviour and segregation of DS IN738 superalloy

The effect of boron and zirconium on the directional solidification behaviour and segregation of IN738 superalloy has been studied. It was found that additions of boron and zirconium enlarge the solidus-liquidus temperature interval and increase the amount of residual melt during solidification. Boron gives the alloy a tendency to form developed dendrites, while zirconium enhances a cellular solidified structure. Both boron and zirconium are shown to be rejected to the residual melt during solidification, and shown to change the segregation of alloying elements by interaction.

An electron microscopy study of the reverse transformation behavior of stress-induced martensite in an Fe-Mn-Si alloy

Abstract The effect of prestrain on reverse transformation and shape memory effect (SME) in an Fe-Mn-Si alloy was studied through microscopic analysis by TEM and HREM. It was found that the stabilization of ϵ-martensite at intersections is an important cause for the marked variation of A f and decreased SME in the deformed specimen.