35CrMo钢表面铁基激光熔覆层的组织和耐磨性能

采用CO2激光熔覆装置将LC3530铁基粉熔覆在35CrMo钢基体表面,研究了熔覆层的显微组织、硬度和耐磨性能,并与基体的进行对比。结果表明:基体组织为回火索氏体,晶粒尺寸在20μm左右,而熔覆层的组织为均匀细小的等轴晶,晶粒尺寸大多在8μm;基体的平均硬度为254.1HV,而熔覆层的平均硬度为640.5HV,且硬度分布更加均匀;在相同试验条件下,熔覆层试样的磨损量仅为基体试样的1/7,磨损系数是基体试样的1/5,且磨损后熔覆层试样的表面粗糙度较磨损前的大幅下降,表明激光熔覆后35CrMo钢的耐磨性能得到显著提高;基体试样的磨损机制为犁削磨损,而熔覆层试样的磨损机制为微观切削,其优异的耐磨性能与含有铁、铬、钼和碳等元素的高硬度合金碳化物的形成有关。     

Effect of low-pressure carburizing and plasma nitriding on mechanical properties and fatigue endurance limits of low alloy sintered steels

ABSTRACT

Thermochemical treatments like plasma nitriding or surface carburizing are commonly used to enhance surface hardness of steel components. An important difference between these treatments is the temperature at which they are carried out. In the present paper, the surface carburizing was carried out following a recently reported non-isothermal low pressure carburizing (LPC) treatment. In order to gain a comparative view of the effect of different treatments on the microstructure, microhardness, fatigue and impact properties, materials with distinct hardenability and widely used in the industrial production were evaluated. Tests were also carried out using industrially processed components aimed to an application demanding high wear resistance. The microstructural evolution during case hardening was studied by optical and electron microscopy.     

Time-Resolved Structural Kinetics of an Organic Mixed Ionic–Electronic Conductor

The structure and packing of organic mixed ionic–electronic conductors have an especially significant effect on transport properties. In operating devices, this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Toward this end, the steady-state and transient structure of the model organic mixed conductor, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is characterized using multimodal time-resolved operando techniques. Steady-state operando X-ray scattering reveals a doping-induced lamellar expansion of 1.6 Å followed by 0.4 Å relaxation at high doping levels. Time-resolved operando X-ray scattering reveals asymmetric rates of lamellar structural change during doping and dedoping that do not directly depend on potential or charging transients. Time-resolved spectroscopy establishes a link between structural transients and the complex kinetics of electronic charge carrier subpopulations, in particular the polaron–bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic mixed-conductor-based devices, and present the first real-time observation of the structural changes during doping and dedoping of a conjugated polymer system via X-ray scattering.     

Unpatterned Bioactive Poly(Butylene 1,4-Cyclohexanedicarboxylate)-Based Film Fast Induced Neuronal-Like Differentiation of Human Bone Marrow-Mesenchymal Stem Cells

Herein, we present poly(butylene 1,4-cyclohexanedicarboxylate) (PBCE) films characterized by an unpatterned microstructure and a specific hydrophobicity, capable of boosting a drastic cytoskeleton architecture remodeling, culminating with the neuronal-like differentiation of human bone marrow-mesenchymal stem cells (hBM-MSCs). We have used two different filming procedures to prepare the films, solvent casting (PBCE) and compression-moulding (PBCE*). PBCE film had a rough and porous surface with spherulite-like aggregations (Ø = 10–20 μm) and was characterized by a water contact angle = 100°. PBCE* showed a smooth and continuous surface without voids and visible spherulite-like aggregations and was more hydrophobic (WCA = 110°). Both surface characteristics were modulated through the copolymerization of different amounts of ether-oxygen-containing co-units into PBCE chemical structure. We showed that only the surface characteristics of PBCE-solvent-casted films steered hBM-MSCs toward a neuronal-like differentiation. hBM-MSCs lost their canonical mesenchymal morphology, acquired a neuronal polarized shape with a long cell protrusion (≥150 μm), expressed neuron-specific class III β-tubulin and microtubule-associated protein 2 neuronal markers, while nestin, a marker of uncommitted stem cells, was drastically silenced. These events were observed as early as 2-days after cell seeding. Of note, the phenomenon was totally absent on PBCE* film, as hBM-MSCs maintained the mesenchymal shape and behavior and did not express neuronal/glial markers.     

12CrNi3钢外锁止套局部表面激光淬火工艺

利用半导体激光宽带对12CrNi3外锁止套局部进行表面淬火处理,并对处理后的零件进行外观检验、显微组织观察、硬度检测分析和摩擦磨损试验。试验结果表明:采取定光斑方式,激光头到工件表面扫描区域中心点距离375 mm(离焦量为0),工件倾斜22°,激光头倾斜18°,温度1350 ℃,扫描速度9 mm/s,单道扫描后表面平整性最好。表面激光淬火硬化层为750～1000 μm,最浅处为443.1 μm,硬化区组织为极细小马氏体组织,硬度达600～700 HV0.2,是基体硬度的2倍左右, 约为渗碳+淬火态硬度的1.3倍,且相变硬化区耐磨性能明显提高。     

选区激光熔化316L不锈钢的各向组织与性能

对采用选区激光熔化(SLM)制备的316L不锈钢增材制造试样进行了横向、纵向力学性能与微观组织分析。结果表明,增材制造SLM试件亚结构组织由尺寸为0.4 μm左右的胞状组织所构成,组织之间无明显的成分偏析,纵向与横向拉伸强度分别达到808和713 MPa,在经过1050 ℃热处理后,原组织中部分胞状组织消失,纵向及横向强度分别下降到673 MPa及579 MPa,增材制造试样相对传统热轧试样(550 MPa)具有明显的强度优势。SLM试样组织中存在未熔合缺陷,缺陷几何形状的方向性对其在拉应力作用下连接成裂纹有显著影响。热处理后缺陷长度方向与拉伸应力平行的纵向试样伸长率达到47.5%,横向试样伸长率为20%,伸长率指标均显著低于热轧316L钢试样,未熔合缺陷是导致3D打印试件塑性指标降低的主要因素之一。     

两相区配分时间对IQ&P钢组织与性能的影响

以含Cu低碳钢为研究对象,利用SEM、EPMA和拉伸试验研究了两相区配分时间对其组织演变、元素配分以及经IQ&P处理后力学性能的影响,并利用Dictra软件对元素配分行为进行了动力学计算。结果表明,IQ处理后试验钢中的块状马氏体形成于原铁素体区域;随两相区配分时间延长,粒状马氏体数量减少,板条状马氏体之间的间距减小。检测和计算结果的对比显示,C、Mn、Cu 3种元素的相对配分速率与计算结果一致,但实际配分速率低于各自的计算结果。随两相区配分时间延长,经IQ&P处理后试验钢的抗拉强度先增加后减小,而伸长率持续减小;在600 s时达到较好的强塑性匹配,强塑积为16 963.24 MPa·%。     

Processing of AlSi9Cu3 alloy by selective laser melting

ABSTRACT

Additive manufacturing of Al-alloys allows the production of components with a complicated structured shape, geometry composed by lattice structures, internal cooling, etc. The portfolio of Al-alloys for metal additive manufacturing is still under development and is strongly limited, compared to the conventional technology. The alloy AlSi9Cu3 is used in many applications, but its processing details are still missing. The main aim of this paper is to describe the laser process parameters for AlSi9Cu3, processed by SLM technology and manufactured from two powders of different shapes and particle sizes. The tested process parameters were laser power, laser speed, and hatch distance in the range of 100–400?W, 200–1500?mm?·?s^?1 and 90–150?µm. These were tested using a single-track and cube test. Microstructure, mechanical properties and the fatigue of SLM samples were analysed and compared with as-casted material.     

Effects of friction-stir processing with water cooling on the properties of an Al–Zn–Mg–Cu Alloy

An Al–Zn–Mg–Cu (Al-7B04) aluminium alloy in two conditions, i.e. with an artificial aging (7B04-AA) temper and with an annealing (7B04-O) temper, was friction-stir processed using water cooling, and the microstructure and the mechanical properties of the stir zone (SZ) were investigated. Compared with the samples subjected to air cooling, the SZs of water-cooled samples were strengthened, and the degree of strengthening depended on the initial base metal temper. For friction-stir-processed material after an 7B04-O temper, the efficiency of strengthening was relatively high due not only to the refinement of grains and strengthening precipitates but also due to the high solution level in the SZ. In contrast, the slight strengthening of friction-stir-processed 7B04-AA resulted solely from grain refinement.