On the Effects of Hot Forging and Hot Rolling on the Microstructural Development and Mechanical Response of a Biocompatible Ti Alloy

Zr, Nb, and Ta as alloying elements for Ti alloys are important for attaining superior corrosion resistance and biocompatibility in the long term. However, note that the addition of excess Nb and Ta to Ti alloys leads to higher manufacturing cost. To develop low-cost manufacturing processes, the effects of hot-forging and continuous-hot-rolling conditions on the microstructure, mechanical properties, hot forgeability, and fatigue strength of Ti-15Zr-4Nb-4Ta alloy were investigated. The temperature dependences with a temperature difference (ΔT) from β-transus temperature (Tβ) for the volume fraction of the α- and β-phases were almost the same for both Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys. In the α-β-forged Ti-15Zr-4Nb-4Ta alloy, a fine granular α-phase structure containing a fine granular β-phase at grain boundaries of an equiaxed α-phase was observed. The Ti-15Zr-4Nb-4Ta alloy billet forged at Tβ-(30 to 50) °C exhibited high strength and excellent ductility. The effects of forging ratio on mechanical strength and ductility were small at a forging ratio of more than 3. The maximum strength (σ_max) markedly increased with decreasing testing temperature below Tβ. The reduction in area (R.A.) value slowly decreased with decreasing testing temperature below Tβ. The temperature dependences of σ_max for the Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys show the same tendency and might be caused by the temperature difference (ΔT) from Tβ. It was clarified that Ti-15Zr-4Nb-4Ta alloy could be manufactured using the same manufacturing process as for previously approved Ti-6Al-4V alloy, taking into account the difference (ΔT) between Tβ and heat treatment temperature. Also, the manufacturing equivalency of Ti-15Zr-4Nb-4Ta alloy to obtain marketing approval of implants was established. Thus, it was concluded that continuous hot rolling is useful for manufacturing α-β-type Ti alloy.     

Hi-B电工钢长条状二次再结晶晶粒的形成(英文)

热轧是Hi-B电工钢生产中控制织构及析出的最重要环节之一。研究中观察到,与大生产热轧板相比,实验室热轧很容易导致二次再结晶退火后出现沿轧向生长很长的长条晶。为澄清其形成机制,本文对比研究了大生产和实验室热轧及退火后样品中的组织形貌、织构及析出。结果表明,初始粗大晶粒、低的热轧压下量及低的终轧温度导致析出提前发生并沿轧向分布造成二次再结晶退火后长条晶粒及细小的线晶的出现。     

Effects of Cold Rolling Reduction on Microstructure,Thickness, Adhesive Force of Al-Si Coating and on Bending Toughness of Al-Si Coated Press-Hardened Steel

Al-Si coated press-hardened steel (PHS) is widely used along with the development of light-weight vehicles, and the tailor-rolled blank parts based on Al-Si coated PHS have attracted much attention. The preparation process includes cold rolling, austenitization, hot-stamping, and quenching. The most widely used AS60/60 coating will change after cold rolling and austenitization, which has been little-studied. Herein, the effects of cold rolling reduction on the microstructure, thickness, adhesive force of AS60/60 coating and on bending toughness of AS60/60 coated PHS were studied. As the cold rolling reduction ratio increased from 0% to 50%, the coatings were gradually thinned, but the overall continuity was unchanged. When the reduction ratio was 40% or above, rapid diffusion channels were formed. The adhesive force of coatings was 21.50–22.15 MPa. After austenitization, the coating thickness gradually decreased as the cold rolling reduction ratio rose from 0% to 50%, but the structure and overall continuity were both unchanged, and the adhesive force was 21.60–22.40 MPa. The rapid diffusion channels promoted the transition from brittle Fe2Al5 to tough FeAl during austenitization, leading to a rapid increment in bending toughness after Al-Si coated PHS was quenched. When the reduction ratio was 50%, the bending angle was improved by 23%.     

New Platforms Based on Frontal Cellular Automata and Lattice Boltzmann Method for Modeling the Forming and Additive Manufacturing

Materials science gives theoretical and practical tools, while new modeling methods and platforms provide rapid and efficient development, improvement, and optimization of old and new technologies. Recently, impressive progress has been made in the development of computer software and systems. The frontal cellular automata (FCA), lattice Boltzmann method (LBM), and modeling platforms based on them are considered in the paper. The paper presents basic information on these methods and their application for modeling phenomena and processes in materials science. Recrystallization, crystallization, phase transformation, processes such as flat and shape rolling, additive manufacturing technologies (Selective Laser Sintering (SLS)/ Selective Laser Melting (SLM)), and others are examples of comprehensive and effective modeling by the developed systems. Selected modeling results are also presented.     

Effect of Rolling Temperature on Microstructure and Properties of Al-Mg-Li Alloy

In this study, the effects of hot-rolled processes at different temperatures (420 °C, 450 °C, and 480 °C) and subsequent solid solution and aging treatments on the microstructure, mechanical properties, and corrosion properties of Al-Mg-Li alloys with trace Sc and Zr addition were investigated. The aging treatment of rolled sheets after solid solution treatment could obtain Al₃Li particles and Al₃(Sc, Zr)/Al₃Li core–shell particles to improve the mechanical properties of Al-Mg-Li alloy products effectively. The results showed that, as the rolling temperatures increased from 420 °C to 480 °C, the alloy’s ultimate tensile strengths and yield strengths increased, while the corrosion resistance decreased. The increase in rolling temperature increased the precipitation-free zone (PFZ) width of the alloy, which undermined the corrosion resistance of the alloy. Moreover, elevating the hot rolling temperature changes the texture strength of the alloy. Particularly in the 480 °C hot-rolled sample, the decrease in the Brass texture strength and the increase in the S texture and Copper texture strength led to an increase in the Taylor factor (M). The increase in rolling temperature also raised the number density of the Al₃(Sc, Zr)/Al₃Li core–shell particles. The presence of such particles not only inhibits grain growth but also changes the strength mechanism from dislocation cutting to Orowan bypassing. Due to the combination effect of grain morphology, texture evolution, and precipitation behavior, the 480 °C hot-rolled sample had the highest properties.     

Study on Symmetry and Asymmetry Rolling of AA2519-T62 Alloy at Room-Temperature and Cryogenic Conditions

The aim of this investigation was to identify the effect of rolling at room temperature and under cryogenic conditions on selected properties and the microstructure of the AA2519-T62 aluminum alloy. The rolling processes were conducted with different variants of asymmetry (1.0—symmetry rolling; 1.2, 1.4 and 1.6). The investigation of the obtained samples involves microhardness distribution, microstrains, and microstructure observations using light and transmission electron microscopes. Both rolling at room temperature and under cryogenic conditions increased the micro-hardness of AA2519-T62 by at least 10%. The highest reported increase (25%) was obtained for the sample rolled at room temperature in the symmetry rolling process. The samples rolled under cryogenic conditions are characterized by a lower increase in microhardness than samples rolled at room temperature and by significantly lower values of microstrains. The application of rolling with the asymmetry ratio remaining within the range of 1.2–16 only slightly affected the microhardness values of the samples rolled at room temperature and under cryogenic conditions with respect to conventional symmetrical rolling.     

A Multiscale Overview of Modelling Rolling Cyclic Fatigue in Bearing Elements

During service, bearing components experience rolling cyclic fatigue (RCF), resulting in subsurface plasticity and decay of the parent microstructure. The accumulation of micro strains spans billions of rolling cycles, resulting in the continuous evolution of the bearing steel microstructure. The bearing steel composition, non-metallic inclusions, continuously evolving residual stresses, and substantial work hardening, followed by subsurface softening, create further complications in modelling bearing steel at different length scales. The current study presents a multiscale overview of modelling RCF in terms of plastic deformation and the corresponding microstructural alterations. This article investigates previous models to predict microstructural alterations and material hardening approaches widely adopted to mimic the cyclic hardening response of the evolved bearing steel microstructure. This review presents state-of-the-art, relevant reviews in terms of this subject and provides a robust academic critique to enhance the understanding of the elastoplastic response of bearing steel under non-proportional loadings, damage evolution, and the formation mechanics of microstructural alterations, leading to the increased fatigue life of bearing components. It is suggested that a multidisciplinary approach at various length scales is required to fully understand the micromechanical and metallurgical response of bearing steels widely used in industry. This review will make significant contributions to novel design methodologies and improved product design specifications to deliver the durability and reliability of bearing elements.     

Tensile Properties and Damping Capacity of Cold-Rolled Fe-20Mn-12Cr-3Ni-3Si Damping Alloy

The tensile properties and damping capacity of cold-rolled Fe–20Mn–12Cr–3Ni–3Si alloys were investigated. The martensitic transformation was identified, including surface relief with a specific orientation and partial intersection. Besides, as the cold rolling degree increased, the volume fraction of ε-martensite increased, whereas α’-martensite started to form at the cold rolling degree of 15% and slightly increased to 6% at the maximum cold rolling degree. This difference may be caused by high austenite stability by adding alloying elements (Mn and Ni). As the cold rolling degree increased, the tensile strength linearly increased, and the elongation decreased due to the fractional increment in the volume of martensite. However, the damping capacity increased until a 30% cold rolling degree was approached, and then decreased. The irregular tendency of the damping capacity was confirmed, depicting that it increased to a specific degree and then decreased as the tensile strength and elongation increased. Concerning the relationship between the tensile properties and the damping capacity, the damping capacity increased and culminated, and then decreased as the tensile properties and elongation increased. The damping capacity in the high-strength area tended to decrease because it is difficult to dissipate vibration energy into thermal energy in alloys with high strength. In the low-strength area, on the other hand, the damping capacity increased as the strength increased since the increased volume fraction of ε-martensite is attributed to the increase in the damping source.     

Prototype Continuous Flow Ventricular Assist Device Supported on Magnetic Bearings

Abstract This article describes a prototype continuous flow pump (CFVAD2) fully supported in magnetic bearings. The pump performance was measured in a simulated adult human circulation system. The pump delivered 6 L/min of flow at 100 mm Hg of differential pressure head operating at 2,400 rpm in water. The pump is totally supported in 4 magnetic bearings: 2 radial and 2 thrust. Magnetic bearings offer the advantages of no required lubrication and large operating clearances. The geometry and other properties of the bearings are described. Bearing parameters such as load capacity and current gains are discussed. Bearing coil currents were measured during operation in air and water. The rotor was operated in various orientations to determine the actuator current gains. These values were then used to estimate the radial and thrust forces acting on the rotor in both air and water. Much lower levels of force were found than were expected, allowing for a very significant reduction in the size of the next prototype. Hemolysis levels were measured in the prototype pump and found not to indicate damage to the blood cells.     

重组人白介素-1对大鼠微血管白细胞滚动与粘附的作用

目的：研究重组人白介素－１α（ＩＬ－１）对大鼠微血管白细胞的滚动与粘附作用。方法：采用高倍显微电视放大技术观察大鼠脊斜肌微循环标本白细胞的变化。结果：ＩＬ－１（０．１２５～０．７５ｍｇ·ｋｇ－１）ｉｐ后显著促进微血管中白细胞的滚动与粘附，有明显的量效关系。白细胞的滚动在给药（０．５ｍｇ·ｋｇ－１）３ｍｉｎ后从正常４±１增至７８±９．０个·ｍｉｎ－１。粘附于微血管壁的白细胞在ＩＬ－１给药３０ｍｉｎ后，从正常每８０μｍ血管１．０±１．０增至１４．０±３．０个。结论：ＩＬ－１促进大鼠脊斜肌微循环中的白细胞滚动与粘附。