Symmetry-breaking transitions in equilibrium shapes of coherent precipitates: Effect of elastic anisotropy and inhomogeneity

We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems under a plane-strain condition with the principal misfit strain components ε* _xx and ε* _yy . For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε* _yy /ε* _xx . We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness; moreover, the transition is also forbidden when the particle stiffness is greater than a critical value.     

On the equilibrium silicide in beta Ti-V alloys containing Si

The addition of small amounts of silicon (usually less than R ~1 at. pct) to strengthen α(hcp)-β(bcc) and martensitic Ti alloys is well established. The equilibrium suicide formed in these alloys has been identified as hexagonal Ti₅Si₃ (Refs. 1, 2) (or (Ti,Zr)₅Si₃ phase in alloys containing Zr), although there is also a report of a tetragonal Ti₃Si phase. The use of Si to age harden β Ti alloys, specifically Ti-V-Si alloys, has also been reported. While the precipitation sequence in these alloys involves an identifiable hexagonal     

Formation of ordered precipitates in Al-Sc-Er-(Si/Zr) alloy from first-principles study

The nucleation properties and stability of the ordered precipitates in Al-Sc-Er alloy were extensively studied by first-principles calculation. The calculated substitutional formation energy reveals that the dissolved Sc or Er in the Al matrix is very favorable to substitute the X sublattice site in L1₂-Al₃X (X = Sc/Er). The calculated solubility curve demonstrates the significant contribution of vibrational entropy to nucleation. The interface energies for Al/Al₃Sc, Al/Al₃Er and Al₃Sc/Al₃Er were calculated in the three directions of [100], [110] and [111], and we find that the interface structure in (100) plane is the most desirable, and the interface energy of Al/Al₃Er is the largest. Regardless of temperature and Sc/Er ratio, the L1₂-Al₃Sc_xEr_1-x precipitation phase mainly forms as the core-shell structure with Al₃Er as the core and Al₃Sc as the shell due to lower nucleation energy. The core-shell structure behaves higher stability once the particle radius is greater than 1 nm. Furthermore, the thermodynamic driving force for the segregating of Si or Zr in Al-Sc-Er alloy should accelerate the precipitation kinetics, where Si partitions occur preferentially to the Al₃Er and Zr partitions preferentially to the Al matrix. Overall, these theoretical results can offer solid explanations to the available experimental results.     

Texture evolution by grain growth in the presence of MnS and AIN precipitates in Fe-3% Si alloy

Texture evolution by grain growth in the presence of MnS and AIN precipitates in Fe-3% Si alloy was investigated by X-ray diffraction and electron channelling technique. Two texture groups A and B evolved from the primary texture (grain diameter of 6 μm) composed mainly of {111} 〈112〉 oriented grains. The group A (grain diameter of 2600 μm) were mainly composed of two subgroups, one with Goss oriented grains and another with Goss oriented grains rotated around ND axis by about 15 and 20°, while the group B (grain diameter of 700 μm) had an intensity level of about one seventh of that of the group A and had orientations centering around {112} 〈110〉. The ideal Goss or near Goss oriented grains of group A were infrequent in the primary recrystallized structure and made few Σ1 boundaries. They made large numbers of Σ9 boundaries though, or had a large value of the product (number of grains at orientation × number of σ9 boundaries made by them). The grains in orientations within the texture group B were fairly frequent in the primary structure and made large numbers of Σ1 boundaries. The value of the product (number of grains at orientation × number of Σ9 boundaries made by them) was large. The mechanism of the evolution of the A and B groups is considered to be due to (1), the higher mobility, in the presence of precipitate inhibitors, of adjacent grains in Σ9 coincidence or in coincidence orientations with a 〈110〉 rotation axis; (2), because Σ1 related grains are stable and less mobile under these conditions.     

Resistance to shape refinement of precipitates in Al-(Si,Ge) alloys during thermal cycling

The present work addresses the response of Si-Ge precipitates in Al-0.5Si-0.5Ge (at. pct) to thermalcycling treatments of the sort known to refine the shapes of Ge precipitates in binary Al-Ge alloys. Alloys aged at 250 °C contained both small, platelet precipitates on {111} planes and larger, equiaxed precipitates that were heavily twinned. Thermal cycling between 250 °C and 360 °C led to partial or complete dissolution of the platelets. However, the equiaxed particles coarsened at an essentially constant shape; the shape refinement that led to untwinned, single-variant octahedral precipitates in binary Al-Ge did not occur. The apparent reason is the heavy twinning of the Si-Ge precipitates, which produces particles with a nearly spherical shape and rounded, incoherent interfaces and is, hence, a viable mechanism for relaxing the large misfit strain of the precipitate structure. The twinned particles undergo normal coarsening at an essentially constant shape. After thermal cycling, the precipitates contain Si and Ge in the approximate ratio of 70Si-30Ge, which is in the composition range expected for the cycling temperature.     

热轧加热温度对3.0 %Si无取向硅钢组织及析出物的影响

研究了热轧加热温度对Si的质量分数3.0 %的无取向硅钢的热轧和常化组织及析出物的影响规律。结果表明：热轧组织沿厚度方向存在组织梯度、析出物呈球状和不规则形状分布在晶内;随着热轧加热温度的提高,中间层纤维状变形带宽度变窄;加热温度为1 150 ℃时,小于100 nm的AlN析出粒子数量增加。热轧板经900 ℃常化后,为完全再结晶铁素体组织,组织均匀性提高、析出物聚集和粗化;提高热轧板加热温度,常化组织的平均晶粒尺寸降低,大于100 nm的析出物和20~100 nm的 AlN、AlN+Ti复合析出相数目逐渐增多。     

Dopant particle characterization and bubble evolution in aluminum-potassium-silicon-doped molybdenum wire

The present article describes the creation of dopant inclusions in aluminum-potassium-silicon (AKS)-doped molybdenum powder and the generation of potassium bubbles in doped molybdenum wire. Molybdenum wire is used extensively in the incandescent lamp industry for coiling mandrels, filament support wires, and foil seals. The AKS-doped molybdenum wire is an important product, because it possesses greater high-temperature strength and a higher recrystallization temperature than undoped molybdenum; both of these properties are important for structural applications in lamps. The AKS-doped molybdenum wire is produced in a similar manner to AKS-doped tungsten wire, but lower processing temperatures are typically used for the production of molybdenum wire. Previous studies on AKS-doped tungsten wire have shown that the dispersion which provides the interlocking grain structure in recrystallized tungsten wire is bubbles of elemental potassium; these enhance incandescent lamp filament life. However, there is little previous work on the potassium-containing dispersion in AKS-doped molybdenum wire. In AKS-doped molybdenum, the dispersion can be either potassium bubbles, or solid oxide particles, depending on the processing method. This article will describe a series of analyses of doped molybdenum wire and its precursors, namely, doped powder and sintered ingots. The roles of high- and low-temperature sintering are also described.     

高浓度载体浮选工艺提高磨浮处理能力的试验研究与技术改造

某黄金矿山针对其规模的不断扩大,但受到场地的限制,配套设备不能无限制扩大,造成浮选矿浆浓度高、粒度粗等问题,进行了一系列工艺参数的优化及相应技术改造,确定了适宜的药剂制度,保证了较高的金回收率。技术改造后,该矿山选矿厂累计处理矿石量899 755 t,获得浮选尾矿品位低于0.115 g/t,富集比19.16倍,金浮选回收率95.34%的较好指标。     

On the elastic interaction of hydrogen with precipitates in lath martensite

The interaction of hydrogen with dislocations is well established, but its interaction with other structural features in a material has not been investigated or discussed to any appreciable degree. It is the intent of this discussion to examine the preference of precipitates for hydrogen atoms in a plain carbon steel, which is quenched to a martensitic structure and tempered. This structure represents one of the most susceptible to hydrogen embrittlement in the as-quenched condition and the most resistant in the highly tempered condition. One of the prominent features of this microstructure is the carbide precipitate and its transformational and morphological changes that result on tempering. The ability for trapping hydrogen, from an elastic energy standpoint, is seen to decrease with increasing loss in coherency of the precipitate. An energy for interaction between coherent precipitates and hydrogen atoms is calculated.     

Relation between formability and precipitates in Ti-IF enamelling steels

The influence of steel composition and processing conditions on the nature of precipitates in Ti interstitial free (IF) steels for enamelling were investigated in detail. Steels designed for enamelling applications require a higher amount of precipitates than conventional deep drawing IF steels, e.g. for automotive applications. Formable IF grades for enamelling applications have high Ti, S and C contents and the properties have hitherto not been investigated in detail. This work focused on the correlation between precipitate nature, texture development and deep drawability. It was found that a low reheating temperature, a high coiling temperature and a C/S ratio in the range of 0.4–0.5, favoured the beneficial precipitation of Ti₄C₂S₂. Furthermore, it is shown that for a steel with a given C/S ratio, a high Ti₄C₂S₂/Ti₄S₅-ratio resulted in improved deep drawability. The deep drawability decreases with increasing C/S ratio. This is due to the decrease in γ-fibre intensity, caused by an increased amount of TiC-precipitates.