Although the austenitic stainless steels 304 and 321 are often treated nominally as equivalents in their hot rolling characteristics, the question remains whether any subtle differences between the two allow further optimisation of their respective hot rolling schedules. The hot workability of these two types of austenitic stainless steels were compared through single-hit Gleeble simulated thermomechanical processing between 800℃ and 1200℃ while the strain rate was varied between 0.001/s and 5/s. It was found that the constants for the hyperbolic sine equation for hot working of 321 steel are 465 kJ/mol Q = , 17 1 1 3

The γ-TiAl intermetallic alloy doped with Nb, Cr, and Si metals has been developed.It has emerged that the ternary Ti-48Al-2Nb and quinary Ti-48Al-2Nb-0.7Cr-0.3Si alloys yielded the best mechanical and cyclic oxidation properties. In particular, the quinary Ti-48Al-2Nb-0.7Cr-0.3Si alloy rapidly developed the protective stable Al 2 O 3 oxide doped with nitrogen and titanium oxynitride during cyclic oxidation. This showed a lower hardness when compared to the other alloys after cyclic oxidation.The oxide layer proved to have a good adhesive relationship with the parent metal.The alloys microstructures were analysed with the scanning electron microscopy (SEM). The sample hardness test were conducted by Vickers hardness tester. Research Highlights• Ti-48Al, Ti-48Al-2Nb, Ti-48Al-2Nb-0.7Cr and Ti-48Al-2Nb-0.7Cr-0.3Si were developed.• Ti-48Al-2Nb and Ti-48Al-2Nb-0.7Cr-0.3Si has excellent mechanical properties• Ti-48Al-2Nb and Ti-48Al-2Nb-0.7Cr-0.3Si revealed best cyclic oxidation resistance.• Formation of oxynitrides mixed with Al 2 O 3 /TiO 2 was detected.for scientists and engineers aiming to minimise the effect of both oxidation and oxygen embrittlement when these materials are in applications. One of the γ-TiAl intermetallic competitive material for high temperature applications are NiAl alloys [1-3]. Different approaches have been adopted to resolve the high temperature oxidation, leading to the development of coatings to prevent detrimental environmental effect on these alloys [4-6].The heat and creep-resistant intermetallic substrates deposited with nanocrystalline γ-TiAl intermetallic TiAl-based coatings micro-alloyed with Cr atoms induced very good oxidation resistance at 1173 K [4]. Furthermore, TiAl 3 /Al 2 O 3 composite powders were prepared by high energy ball milling and subsequent heat-treatment. The TiAl 3 /Al 2 O 3 powders deposited on γ-TiAl intermetallic and decreased the oxidation rate of γ-TiAl substrate [7] and Cr 2 AlC coatings with better Al rich oxide scale [8]. The laser aided manufacturing of γ/β-Al 2 O 3 coating on NiCrAlY coatings proved to withstand the operating temperature of 1200°C for ten cycles [9]. Additionally, another method of improving the properties of γ-TiAl alloys is to modify their chemical composition with alloying elements. For example, doping of traditional high temperature alloys such as β-NiAl to improve cyclic oxidation have been investigated [10-12]. Also, attempts to improve the oxidation resistance of Ti-Al intermetallic phase based alloys showed positive results [13-17]. Ding et al, [18] further investigated Nb-doped TiAl for cyclic deformation and microstructure evolution of high Nb containing TiAl alloy during high temperature low cycle fatigue. Our current investigation focus on the innovative alloying elements to produce the binary, ternary, quaternary and quinary alloys by addition of the Nb, Cr and Si γ-Ti-Al alloys. The arc button melting performed under vacuum was employed to manufacture the four γ-TiAl based alloys of nominal composition binary Ti-48Al (at. ...

No abstract

The -Ti-45Al-2Nb-0.7Cr-0.3Si based intermetallic alloy was developed. Microstructure evolution of the as-cast and heat-treated alloy yielded the spheriodised and Widmanstätten laths. High temperature differential thermal analysis (HTDTA) was performed on the as-cast Ti-45Al-2Nb-0.7Cr-0.3Si alloy in order to determine critical temperatures and provide insight into phase transformations prior heat treatment. The morphology of the alloy was analysed by the optical microscopy, scanning and transmission electron microscopy (SEM/TEM). The SEM was equipped with energy dispersion spectroscopy (EDS) for chemical composition. The EBSD mapping was employed to determine microstructural evolution. The results show that after heat-treatment the homogeneous microstructures were obtained, compared to the dendritic as-cast structure. The spheriodised laths were seen embedded inside the lamellar structure; whereas the Widmanstätten laths were observed as crossed/needle like ( 2 +) laths of small spacing, with a spatial orientation with respect to the lamellar structure. The structural development was determined by the X-ray diffraction (XRD).

No abstract