The Characteristic of Fe as a β-Ti Stabilizer in Ti Alloys

It is well known that adding elements, especially β-Ti stabilizers, are holding a significant effect on titanium alloy strength due to the solution and precipitate strengthening mechanisms. In order to reveal the Fe strengthening mechanism in titanium, this study investigate the effect of Fe on the stability of β-Ti and the phase transition between α, β and ω phase with first-principle calculations. According to our study, Fe is a strong β-Ti phase stabilizer could owe to the 3d orbital into eg and t2g states which results in strong hybridization between Fe-d orbital and Ti-d orbital. The phase transition from ω to β or from α to β becomes easier for Fe-doped Ti compared to pure titanium. Based on our results, it is found that one added Fe atom can lead the phase transition (ω → β) of at least nine titanium atoms, which further proves that Fe has a strong stabilizing effect on β-Ti phase. This result provides a solid guide for the future design of high-strength titanium with the addition of Fe.

Effect of cold rolling and ageing treatment on the interface morphology and mechanical properties of maraging steel/medium-entropy alloy multilayer composite

The cold rolling and subsequent ageing treatment of hot-rolled 18Ni300/CoCrNi multilayer composites were carried out to analyse the high work hardening ability of medium-entropy alloy (CoCrNi alloy) and the ageing precipitate strengthening effect of maraging steel (18Ni300). The results show that with the rise of cold rolling reduction, the ratio constitute layer and interface transition layer thicknesses are gradually decreased, and the interface shape changes from a flat to a wavy state, which is mainly due to the serious work hardening of the CoCrNi layer. Meanwhile, the tensile strength continuously increased. When the multilayer composite is cold-rolled to 0.5 mm, its tensile strength reaches more than 2 GPa, and the fracture elongation remains at approximately 7%. After ageing, the superior tensile strength is as high as 2825 MPa, which is attributed to the synergistic effect of work hardening, precipitation strengthening and strong interface bonding strengthening.

Effect of Heat Treatment Process on Mechanical Properties and Microstructure of S280

The effect of solution temperature and aging temperature on mechanical properties and microstructure of the new ultrahigh strength stainless steel S280 was investigated by heat treatment process experiment. The results showed that the optimal heat treatment process was as follows: heating to 1080 °C，holding for a hour, and quenching in oil; cooling to -73 °C, holding for 2 hour, and warming in air to room temperature; heating to 540~550 °C, holding for 4 hour, and cooling in air. Choosing this heat treatment process, the steel can get good coordination between strength and toughness. Analyzed by HREM, the steel had desirable microstructures, which were fine lath martensite matrix with high density dislocation and finely dispersed precipitate strengthening phase, and film-like reversed austenite precipitated from the boundary of martensite.

Precipitation-dependent corrosion analysis of heat treatable aluminum alloys via friction stir welding, a review

Although the various advantages of novel Friction stir welding (FSW) process; the weld surfaces are subjected to various serious problems such as lower corrosion resistance, high susceptibility to stress corrosion cracking and poor joint fatigue strength due to complex material flow and severe plastic deformation during the welding process. Corrosion behaviour of friction stir welded (FSWed) precipitate strengthening Al alloys have significant impact on metallurgical and electrochemical properties of structures. In FSW of precipitate strengthening Al alloys the localized heat input and severe plastic deformation creating appreciable changes in microstructure and modifies the microchemistry and metallurgical characteristics of precipitates. The heterogeneous distribution of precipitates and precipitate free zones (PFZs) along the grain boundaries leads to variation in electrochemical behaviour across the weld zones and hence increasing the susceptibility of weld surface to various corrosion attacks such as intergranular corrosion, pitting corrosion, exfoliation corrosion, stress corrosion cracking and galvanic corrosion. However, the corrosion resistance of FSWed joints can be improved either by reducing the size or redissolve the coarsened precipitates within the joint or modifying the microchemistry by controlling the size, location and distribution of precipitates which largely determine the corrosion rate of the weld surfaces. Consequently, it is imperative to address the influence of material modifications during FSW on corrosion behaviour of weld surface. This review paper addresses the precipitate dependent corrosion behaviour of FSWed joints of heat treatable/precipitate strengthening Al alloys and the various effective methods either to reduce or eliminate the effect of corrosion attack in FSWed joints of heat treatable Al alloys.