Erratum to: Grain Refinement by Cyclic Displacive Forward/Reverse Transformation in Fe-High-Ni Alloys

Metallurgical and Materials Transactions A -     

Microstructures and Grain Refinement of Additive-Manufactured Ti-xW Alloys

Metallurgical and Materials Transactions A - It is necessary to better understand the composition–processing–microstructure relationships that exist for materials produced by additive...     

Grain Refinement of Alloys in Fusion-Based Additive Manufacturing Processes

Metallurgical and Materials Transactions A - One of the less desirable aspects of fusion-based additive manufacturing is the propensity for coarse columnar grain structures crossing build layers to...     

Role of Remelting in Grain Refinement of Undercooled Single-Phase Alloys

Metallurgical and Materials Transactions A - Bulk and thin samples of Cu75Ni25 (at. pct) alloy were solidified over a range of undercoolings. Unlike the bulk samples, in which grains were...     

铝合金晶粒细化的研究进展与发展趋势

阐述了铝合金晶粒细化技术的研究和应用现状,铝合金获得细晶的几种凝固技术,晶粒细化剂和变质剂的变质细化作用及晶粒细化机理。并叙述了铝合金晶粒细化的发展趋势以及新型Al-Ti-C-Re、Al-Ti-B-Re合金的细化效果及应用。     

Revisiting the Role of Solutes in Grain Refinement of Hypoeutectic Alloys

Metallurgical and Materials Transactions A - Experimental data on grain size in hypoeutectic alloys with various solute concentrations are collected and analyzed. Curves of grain size as functions...     

铝及铝合金细化剂的研究

综述了晶粒细化剂的发展及历史，细化剂的细化机理和各种细化剂的比较。并着重介绍了新一代的AlTiC晶粒细化剂。     

铝及铝合金细化剂的研究

综述了晶粒细化剂的发展历史及细化剂的细化机理和各种细化剂的比较。并着重介绍了新一代的Al-Ti-C晶粒细化剂。     

Origin of Significant Grain Refinement in Co-Cr-Mo Alloys Without Severe Plastic Deformation

We have previously reported that ultrafine-grained (UFG) microstructures can be obtained in a Co-29Cr-6Mo (wt pct) alloy by utilizing dynamic recrystallization (DRX) that occurs during conventional hot deformation (Yamanaka et al.: Metall. Mater. Trans. A, 2009, vol. 40A, pp. 1980?94). The present study investigates the novel DRX mechanism of this alloy in detail. The microstructure evolution during hot deformation under relatively high Zener?CHollomon (Z) parameter conditions for which ultrafine grains can develop was systematically investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy. This alloy exhibited a different flow stress behavior and microstructural development from conventional DRX mechanisms. The deformation microstructure contained a large number of stacking faults, which implies that planar dislocation slip is the primary deformation mechanism in the hot deformation of the Co-29Cr-6Mo alloy due to its abnormally low stacking fault energy (SFE) at elevated temperatures. Inhomogeneities in local strain distributions induced by planar slip will enhance grain subdivision by geometrically necessary (GN) dislocation boundaries. Deformation twinning may also contribute to grain refinement. The DRX mechanism operating in the Co-29Cr-6Mo alloy is discussed by considering the relationships between anomalous dislocation structures, flow stress behavior, texture development, and nucleation behavior.     

The Role of Carbon in Grain Refinement of Cast CrFeCoNi High-Entropy Alloys

As a promising engineering material, high-entropy alloys (HEAs) CrFeCoNi system has attracted extensive attention worldwide. Their cast alloys are of great importance because of their great formability of complex components, which can be further improved through the transition of the columnar to equiaxed grains and grain refinement. In the current work, the influence of C contents on the grain structures and mechanical properties of the as-cast high-entropy alloy CrFeCoNi was chosen as the target and systematically studied via a hybrid approach of the experiments and thermodynamic calculations. The alloys with various C additions were prepared by arc melting and drop cast. The as-cast macrostructure and microstructure were characterized using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The cast HEAs transform from coarse columnar grains into equiaxed grains with the C level increased to ≥ 2 at. pct and the size of equiaxed grains is further decreased with the increasing C addition. It is revealed that the interdendritic segregation of Cr and C results in grain boundary precipitation of M₂₃C₆ carbides. The grain refinement is attributed to the additional constitutional supercoiling from the C addition. The yield stress and tensile strength at room temperature are improved due to the transition of columnar to equiaxed grains and grain refinement.     

Influence of Mg on Grain Refinement of Near Eutectic Al-Si Alloys

Although the grain-refinement practice is well established for wrought Al alloys, in the case of foundry alloys such as near eutectic Al-Si alloys, the underlying mechanisms and the use of grain refiners need better understanding. Conventional grain refiners such as Al-5Ti-1B are not effective in grain refining the Al-Si alloys due to the poisoning effect of Si. In this work, we report the results of a newly developed grain refiner, which can effectively grain refine as well as modify eutectic and primary Si in near eutectic Al-Si alloys. Among the material choices, the grain refining response with Al-1Ti-3B master alloy is found to be superior compared to the conventional Al-5Ti-1B master alloy. It was also found that magnesium additions of 0.2 wt pct along with the Al-1Ti-3B master alloy further enhance the near eutectic Al-Si alloy’s grain refining efficiency, thus leading to improved bulk mechanical properties. We have found that magnesium essentially scavenges the oxygen present on the surface of nucleant particles, improves wettability, and reduces the agglomeration tendency of boride particles, thereby enhancing grain refining efficiency. It allows the nucleant particles to act as potent and active nucleation sites even at levels as low as 0.2 pct in the Al-1Ti-3B master alloy.     

镁及镁合金晶粒细化的研究现状

叙述了镁及镁合金晶粒细化的几种方法，即合金化法、变质处理法、固态变形处理法、半固态成形法、快速凝固法及熔体搅拌法等。细化镁合金晶粒尺寸能显著提高其力学性能．这对推广镁合金的应用具有重要意义。     

Reverse Austenite Transformation and Grain Growth in a Low-Carbon Steel

Metallurgical and Materials Transactions A - The mechanisms controlling the reverse austenite transformation and the subsequent grain growth are examined in a low-carbon steel during slow...     

Effects of Cooling Rate and Solute Content on the Grain Refinement of Mg-Gd-Y Alloys by Aluminum

The effect of Al additions on grain refinement of Mg-Gd-Y alloys with different solute contents at different cooling rates has been investigated. For all alloys, significant grain refinement was due to the formation of Al₂(Gd _x Y_1?x ) nucleant particles. The number density and size distribution of Al₂(Gd _x Y_1?x ) were affected by both solute content and the cooling rate. Grain sizes (d _gs) of Mg-Gd-Y base alloys and of Mg-Gd-Y-Al alloys were related to solute content (defined by the growth restriction factor, Q), cooling rate ( \( \dot{T} \) ), and area number density (ρ _ns) and size (d _p) of nucleant particles that can be activated. It is found that grain sizes of Mg-Gd-Y base alloys follow the relationship \( d_{\text{gs}} = a + \frac{b}{{Q\sqrt {\dot{T}} }} \) , while grain sizes of Al-refined samples follow the relationship \( d_{\text{gs}} = \frac{a'}{{\sqrt {\rho {}_{\text{ns}}} }} + \frac{b'}{{\sqrt {\dot{T}} Qd_{\text{p}} }} \) , where a, b, a′, and b′ were constants. In addition, the grain refinement effect of Al additions was more susceptible to solute content and the cooling rate than that of Zr which is regarded as the most efficient grain refiner for Mg alloys.     

Criteria of Grain Refinement Induced by Ultrasonic Melt Treatment of Aluminum Alloys Containing Zr and Ti

It is well known that ultrasonic melt treatment (UST) promotes grain refinement in aluminum alloys. Cavitation-aided grain refinement has been studied for many years; however, it is still not being applied commercially. The current article summarizes the results of experimental work performed on various alloying systems at different stages of solidification. The influence of UST parameters and solidification conditions on the final grain structure is analyzed. It was found that small additions of zirconium and titanium can significantly increase the efficiency of UST, under the stipulation that grain refinement is performed in the temperature range of primary solidification of Al₃Zr. The possible mechanisms for this effect are discussed.     

不对称轧制时晶粒细化的研究

研究了不对称轧制晶粒细化问题,结果表明,与对称轧制相比,在相同的变形量下不对称轧制可以使晶粒更细。另外还分析了不对称轧制时,剧烈变形是由于变形区内产生的附加剪切变形和一般压缩变形共同产生的。     

钒氮钢中晶粒细化研究

 采用Gleeble 3500热模拟试验机，在相同工艺条件下，对比研究了钒氮钢、钒钢以及碳锰钢的晶粒细化效果。结果表明，钒氮钢的晶粒细化效果最显著，铁素体的晶粒尺寸可达61 μm，这主要与在奥氏体区中析出的V(C，N)有关。奥氏体区析出的V(C，N)，不但可抑制奥氏体晶粒长大，同时还可以作为铁素体的形核核心，诱导晶内铁素体形成，大大增加铁素体形核率，从而提高了相变细化的比率。     

形变诱导析出在SAF2205超塑组织细化中的作用

运用变形能、相变温度、原始晶粒尺寸与金属组织细化之间的关系,提出了控制σ相析出的新方法.在此基础上,用分段恒温拉伸的方法,对SAF2205钢恒温热拉伸后的性能和微观组织进行了实验研究.研究结果表明:采用变温的恒温热拉伸方法,通过快速冷却,使σ相的析出发生在变形过程中,细小、弥散分布的σ相可以抑制晶粒的长大;为了保证σ相的形变诱导析出,实现双相不锈钢的低温超塑性变形,需要采用较快的冷却速度.