Grain Refinement In Metallic Materials Research Articles

Review on Grain Refinement of Metallic Materials to Regulate Cellular Behavior

Metallic materials have been widely used as orthopedic implants in clinics for their good mechanical, physical, and chemical properties, but their slow osseointegration rate is still one of the main issues causing implantation failure. Grain refinement has recently attracted wide attention for its effective improvement of cell–material interaction for biometals. In this review, the surface and bulk grain refinement mode and the influence of grain size reduction of various metallic materials including titanium, stainless steel, magnesium, zirconium, tantalum, and their alloys as well as NiTi shape memory alloys on the cell responses is summarized in detail. It is hoped that this review could help biomaterials-related researchers to understand the grain refinement of metallic materials in a timely manner, thus boosting the development of biomedical metals for clinical use.

Modelling and simulation of the asymmetric rolling process – establishing the optimal technology parameters to asymmetric rolling

Asymmetric rolling is a technique used to control both the texture and the grain refinement of metallic materials. The aim of asymmetric rolling is to apply a large shear strain uniformly through the thickness of the plate, by maintaining a high degree of friction between the sheet and the rolls. It can be used to improve the formability of material. One of the advantages of asymmetrical rolling is that the rolling force and torque can be decreased. An economic and technological reason, in particular the longitudinally asymmetric rolling is very important to determine the optimum process parameters. The paper presents a method of simulating the asymmetric rolling process. This simulation is carried out to establish the main parameters of rolling particular asymmetric regime. The main goal is to establish a link between the peripheral speed of rolls, pressure and contact length.

Asymmetric rolling process

Abstract Asymmetric rolling is a novel technique used to control both the texture and the grain refinement of metallic materials. The aim of asymmetric rolling is to apply a large shear strain uniformly through the thickness of the plate, by maintaining a high degree of friction between the sheet and the rolls. It can be used to improve the formability of material. One of the advantages of asymmetrical rolling is that the rolling force and torque can be decreased. The methods used for the asymmetric rolling are single roll drive, different work roll speeds, different work roll diameters or different lubricated work roll surfaces.

Scaling up of High-Pressure Sliding (HPS) for Grain Refinement and Superplasticity

The process of high-pressure sliding (HPS) is a method of severe plastic deformation developed recently for grain refinement of metallic materials under high pressure. The sample for HPS is used with a form of sheet or rod. In this study, an HPS facility with capacities of 500 tonnes for vertical pressing and of 500 and 300 tonnes for horizontal forward and backward pressings, respectively, was newly built and applied for grain refinement of a Mg alloy as AZ61, Al alloys such as Al-Mg-Sc, A2024 and A7075 alloys, a Ti alloy as ASTM-F1295, and a Ni-based superalloy as Inconel 718. Sheet samples with dimensions of 10 to 30 mm width, 100 mm length, and 1 mm thickness were processed at room temperature and ultrafine grains with sizes of ~200 to 300 nm were successfully produced in the alloys. Tensile testing at elevated temperatures confirmed the advent of superplasticity with total elongations of more than 400 pct in all the alloys. It is demonstrated that the HPS can make all the alloys superplastic through processing at room temperature with a form of rectangular sheets.

Tensile Yield Strength of a Material Preprocessed by Simple Shear

Modern techniques of severe plastic deformation (SPD) used as a means for grain refinement in metallic materials rely on simple shear as the main deformation mode. Prediction of the mechanical properties of the processed materials under tensile loading is a formidable task as commonly no universal, strain path independent constitutive laws are available. In this paper, we derive an analytical relation that makes it possible to predict the mechanical response to uniaxial tensile loading for a material that has been preprocessed by simple shear and, as a result, has developed a linear strain gradient. A facile recipe for mechanical tests on solid bars required for this prediction to be made is proposed. As a trial, it has been exercised for the case of commercial purity copper rods. The method proposed is recommended for design with metallic materials that underwent preprocessing by simple shear.

High-cycle fatigue bending strength of rapidly solidified and plastic consolidated RS442 aluminium alloy

Grain refinement in metallic materials down to submicro and nano scale results in improvement of mechanical properties. However, increase in strength under static load is not always accompanied by improved fatigue behaviour. In the current studies microstructure and mechanical properties of the submicrocrystalline RS442 aluminium alloy (chemical composition corresponds to conventional 442 cast alloy) were investigated. The alloy was subjected to rapid solidification followed by the extrusion process (variant 1) and additional annealing at 450 °C (variant 2). Rapidly solidified alloy was also consolidated with addition of graphite (variant 3). As the reference material conventionally cast and extruded alloy was also tested (variant 4). For all material variants strength properties were tested in static tensile test and high-cycle stress-controlled fatigue bending tests. It was found that rapid solidification and plastic consolidations led to increase of static mechanical properties of 442 alloy but reduced its fatigue strength.

Damaging Prediction of Difficult-to-Work Aluminum Alloys During Equal Channel Angular Pressing

Severe plastic deformation (SPD) is a well-established method in the recent years for grain refinement in metallic materials. Equal channel angular pressing (ECAP) is one of the most effective SPD techniques. Inherent failures of ECAP, consisting in billet damage, take place if not made a correct process design. In this article, the evolution of damaging for a difficult-to-work Al-Mg alloy during ECAP was investigated. A tridimensional finite element analysis was performed for four different die designs to study the influence of die geometry and process parameters on billet damaging. To validate modeling we used, load level and strain distribution were depicted. Experimental tests were performed to test the numerical prediction. The results show that cracking may be reduced or eliminated by inner fillet corner of the die channels. It was demonstrated that the predicted results were in good agreement with experimental data obtained for 5052 aluminum alloy. The direct effect of knowledge about load and damaging during ECAP is to prevent both tool and billet damage.

Preparation of ultrafine-grained twin-roll cast AlMg3 sheets by accumulative roll bonding

Abstract Accumulative roll bonding is a method for achieving grain refinement of metallic materials by severe plastic deformation, resulting in strength superior to that of conventionally manufactured sheets. The method has been successfully used by the authors to prepare bulk ultrafine-grained sheets from pure aluminium and several twin-roll cast aluminium alloys. The present paper summarizes the results of a study aimed at monitoring the evolution of microstructure and mechanical properties during the accumulative roll bonding process of a twin-roll cast AlMg3 (AW – 5754) alloy. Moreover, the annealing behaviour of the roll-bonded sheets is compared with the behaviour of conventionally rolled counterparts.

Recent development in grain refinement by hydrostatic extrusion

Hydrostatic extrusion is an efficient method of grain refinement to the nanometer scale in metallic materials. The paper shows that it can be used directly to obtain a mean grain size smaller than 100 nm with a significant fraction of high angle grain boundaries in aluminum alloys, titanium, and iron. It is also demonstrated that grain size reduction to this level in some other materials, e.g., nickel, requires a combination of hydrostatic extrusion (HE), as the final operation, after some other methods of severe plastic deformation (SPD). Grain refinement in metallic materials by HE has a significant effect on their properties with a significant increase in mechanical strength and improvement of wear and corrosion resistance while maintaining an acceptable level of plasticity.

연속 회전 등통로각압축 공정의 유한요소해석

Although equal channel angular pressing (ECAP), imposing large plastic shear strain deformation by moving a workpiece through two intersecting channels, is a promising severe plastic deformation method for grain refinement of metallic materials, its batch type characteristic makes ECAP inefficient for multiple-passing. Rotary-die ECAP (RDECAP) proposed by Nishida et al. can achieve high productivity by using continuous processing without taking out the samples from the channel. However, plastic deformation behavior during RD-ECAP has not been investigated. In this study, material plastic flow and strain hardening behavior of the workpiece during RD-ECAP was investigated using the finite element method. It was found that plastic deformation becomes inhomogeneous with the number of passes due to an end effect, which was not found seriously in ECAP. Especially, decreasing corner gap with increasing the number of passes was observed and explained by the strain hardening effect.

Continuous Grain Refinement Using Severe Torsion Straining Process

This study presents a new rapid continuous process for grain refinement in metallic materials through severe plastic deformation (SPD). The new process, designated in this study the severe torsion straining process (STSP), is applicable to a wide range of alloys based on aluminum, magnesium and copper including carbon steel. This process consists of producing a local heated zone in a rod and cooling both sides of the heated zone by spray water while rotating one end with the other. Thus, torsion strain is introduced in the local heated zone. The STSP can be continuous because the straining is achieved while the rod is shifted along the longitudinal axis of the rod. Furthermore, the process requires no die, suggesting a potential for commercialization of grain refinement through SPD. In this study, STSP was applied to an Al-Mg alloy and a Mg-Al-Zn alloy. It is shown that STSP is effective for both alloys so that the grain size is reduced to ~1.5 μm for the Al alloy and ~0.9 μm for the Mg alloy. Tensile testing showed that the strength is increased with a minimal decrease in uniform elongation. There is a critical ratio between rotation speed and moving speed, which defines the feasibility of STSP operation without breaking the rod. The grain size tends to be lowered as the ratio is close to the critical value.

Hydrostatic Extrusion as a Method of Grain Refinement in Metallic Materials

The paper describes hydrostatic extrusion (HE) as a method of grain refinement of metallic materials down to the nanometric scale. The main features of this method are: (a) large strain, (b) very high strain rates (even greater than 104 s-1), and (c) deformation homogeneity. HE offers also the opportunity of obtaining bulk materials in a variety of forms (rods and wires of complex cross-sections, small tubes). The study undertaken on 4 materials (aluminium, aluminium alloy, copper and titanium) has shown that significant grain refinement , down to nanometric scale in the case of titanium and aluminium alloy, occurred during HE processing. This grain refinement produces significantly improved mechanical properties. It has been found that HE offers good prospects for the production of nano-structured metals and alloys.

Development of Severe Torsion Straining Process for Rapid Continuous Grain Refinement

This study presents a rapid continuous process for grain refinement in metallic materials through severe plastic deformation (SPD). The principle is described and the process is applied to an Al-5056 alloy and an S45C carbon steel. The new process, designated in this study the severe torsion straining process (STSP), consists of producing a local heated zone in a rod and introducing torsion strain into the zone by rotating one end with the other. The process is continuous because the straining is achieved while the rod is moved so that the heated zone is shifted along the rod. The STSP does not require the use of any die and can be applicable to pipes or wires. Fine-grained structures produced with the STSP are confirmed using optical microscopy and transmission electron microscopy. Tensile properties are measured and compared with the unstrained fully annealed samples. The feasibility of the STSP is discussed with respect to the rotation speed and moving speed.

Processing of ultrafine ferrite steels

Recently, the grain refinement of metallic materials has been investigated intensively. There are two basic methods, i.e., severe plastic deformation and thermomechanical processing, to refine grain sizes of bulk steels for the ultrafine or submicron range. By severe plastic deformation submicron-grained microstructure (less than 1 μm) in steels can be obtained. For example, the microstructure with ultrafine grains of 0.3 μm in a commercial 0.15 wt.%C–1.1 wt.%Mn–0.25 wt.%Si steel was obtained after ECAP at an accumulative strain of about 4, and the microstructure with ultrafine grains of 0.4 μm in a Ti-added interstitial free (IF) steel was obtained after ARB at an accumulative strain of about 5.6. As a result of thermomechanical processing for the grain refinement, the ultrafine ferrite (UFF) grains (about 1 μm) of steels could be obtained through hot rolling in the intercritical region, warm rolling in the ferrite region, or strip rolling under the condition of strain-induced transformation from austenite to ferrite. A composite microstructure, consisting of UFF grains in the surface layers penetrated to about one-quarter to one-third of thickness and coarser ferrite (about 5–10 μm) and pearlite in the core of the strip, is introduced by strain-induced transformation. Finally, the relationship of strength and ductility is discussed. The strength of ultrafine-grained steels increases with decreasing ferrite grain sizes, following the Hall–Petch relationship. On the other hand, ductility decreases with decreasing ferrite grain sizes. The composite microstructure of UFF surface and coarser core in steels has an advantage to keep both high strength and high ductility.