•The Laves eutectic of INCONEL718 alloy is eliminated via this forming procedure.•Deformation and holding with lower liquid fraction will be more effective in this method.•The mechanism relies on homogenization effect during the deformation and holding process.An energy efficient method called deformation and holding process (DHP) in two phase region, which applied for eliminating the harmful Laves eutectic (LE) phase of INCONEL 718 (IN718) was proposed based on semi-solid forming technology. To verify its feasibility, the effects of solid-liquid fraction and isothermal holding on formation of LE and the microstructure of the deformed alloys were investigated experimentally. LE can be eliminated and the microstructure is refined when deformation and holding were carried out at the end of solidification. The fraction of the LE decreases from about 10.8% in the as-cast specimens to 2.53% in the deformed specimens (0.1/s 50% compression at 1700 °C following 2 min isothermal holding process).

The mesoscopic modeling developed rapidly in the past three decades is a promising tool for predicting and understanding the microstructure evolution at grain scale. In this paper, the recent development of mesoscopic modeling and its application to microstructure evolution in steels is reviewed. Firstly, some representative computational models are briefly introduced, e.g., the phase field model, the cellular automaton model and the Monte Carlo model. Then, the emphasis is put on the application of mesoscopic modeling of the complex features of microstructure evolution, including solidification, solid-state phase transformation, recrystallization and grain growth. Finally, some issues in the present mesoscopic modeling and its perspective are discussed.

Though extensively studied, hardness, defined as the resistance of a material to deformation, still remains a challenging issue for a formal theoretical description due to its inherent mechanical complexity. The widely applied Teter’s empirical correlation between hardness and shear modulus has been considered to be not always valid for a large variety of materials. The main reason is that shear modulus only responses to elastic deformation whereas the hardness links both elastic and permanent plastic properties. We found that the intrinsic correlation between hardness and elasticity of materials correctly predicts Vickers hardness for a wide variety of crystalline materials as well as bulk metallic glasses (BMGs). Our results suggest that, if a material is intrinsically brittle (such as BMGs that fail in the elastic regime), its Vickers hardness linearly correlates with the shear modulus (Hv = 0.151G  ). This correlation also provides a robust theoretical evidence on the famous empirical correlation observed by Teter in 1998. On the other hand, our results demonstrate that the hardness of polycrystalline materials can be correlated with the product of the squared Pugh’s modulus ratio and the shear modulus (Hv=2(k2G)0.585−3Hv=2(k2G)0.585−3 where k = G/B is Pugh’s modulus ratio). Our work combines those aspects that were previously argued strongly, and, most importantly, is capable to correctly predict the hardness of all hard compounds known included in several pervious models.One sentence for highlighted figure: Vickers hardness has been theoretically evidenced to correlate successfully with shear modulus for various bulk metallic glasses (BMGs, left panel) and with a product of the squared Pugh’s modulus ratio and shear modulus for a wide variety of polycrystalline materials (including all superhard materials known, right panel).Highlights► This work derived a theoretical formula of Vickers hardness linearly correlated with shear modulus for various bulk metallic glasses. ► This work derived a theoretical formula to predict Vickers hardness of a wide variety of polycrystalline materials. ► This work generalized the hardness formula through a thorough comparison for BMGs and polycrystalline materials. ► This work validated the powerful prediction of the proposed hardness formula. ► This work highlighted a comparison of several semi-empirical hardness models with the currently proposed formula.

Solid steel balls were added to the melt during the pouring process. A reference 500 kg steel ingot with no addition of solid balls was poured to provide a realistic comparison with the typical macrosegregation found in conventional industry heavy ingots. The experiments show that by adding solid balls the degree of macrosegregation is reduced, the formation of A-type segregation is prevented, a generally refined microstructure is obtained and the mechanical properties are improved. Numerical simulation of the solidification process confirms that the addition of solid balls increases the cooling rate, imposing large temperature gradient which refine the microstructure and alleviate the extent of macrosegregation.

Two-dimensional cellular automaton modeling has been performed to investigate the mechanism of ferrite refinement during the dynamic strain-induced transformation (DSIT) from austenite (γ) to ferrite (α) in a low-carbon steel. The simulated results indicate that the refinement of ferrite grains derived from the DSIT could be interpreted in context of “un-saturated” nucleation and limited growth.

The mould filling process and solidification of TiAl exhaust valves by centrifugal investment casting have been simulated. Two types of runner and gating systems are designed and analysed. In the preliminary design, a “tree-type” set up system is used and a significant amount of porosity is found in many valves of the simulation result. The fluid field simulations indicate that moulds are not filled well in the preliminary design, leading to the last hot spots deviating from the center line of castings. Casting defects deviated from the center line of the part, and the degree of deviation is affected by the mould filling process and temperature fields. Simulation results reveal that castings do not experience sequential solidification, so the design is not proper for the exhaust valve. Comparing the experimental and simulation results, the range of Niyama criterion in the centrifugal TiAl casting is defined, which is 0.14–0.20. Several key factors such as pouring temperature, mould temperature and rotation speed are studied in detail. An optimized design is developed in which valves are rearranged to reduce the neighboring heat radiation effect, and the gate size is enlarged to keep the feeding path open. Sound exhaust valves have been produced successfully using the optimized technique.

In investment foundries, it is usual to pay relatively little attention to the design of the filling system of a casting. Vacuum-cast turbine blades represent a typical case, where the mould filling process is poorly controlled, the mould cavities themselves often being top-filled. The consequential surface turbulence causes the entrapment of oxide film on the liquid surface, despite the use of vacuum melting and pouring. In this work, bottom filling principles were used to minimize turbulence. X-ray radiographic video was used to observe and compare the filling of both bottom- and top-filled moulds. Ni-based alloy investment-cast blades melted and cast in vacuum clearly validated the bottom filling design. Compared to conventional top filling in vacuum, dye penetrant indications were reduced by approximately a factor of 10, and hot cracking appeared to be eliminated.