Effect of electron beam surface hardening on fatigue crack growth rate in AISI 4340 steel

This paper studies the effect of electron beam (EB) surface hardening on the fatigue crack growth rate in AISI 4340 steel. The heat treatment conditions were varied to consider the influence of microstructure and residual stress. The results show that increasing the EB heat input increases the compressive residual stress in the hardened layer. Thus EB surface-hardening treatment improves the fatigue crack growth resistance. This effect increases with increasing EB heat input but disappears as the ΔK value increases. The fracture mechanism of the hardened layer is intergranular fracture, while that of the base material is transgranular quasi-cleavage.     

Surface treatment of 0.20% C carbon steel by high-current pulsed electron beam

A high-current pulsed electron beam（HCPEB） generated on the system of Nadezhda-2 was applied to improve the microstructure and performance of 0.20% C low carbon steel. Surface layers of the samples bombarded by explosive electron beam at different pulses was observed by using electron microscopy. The physical model of the thermal-stress process and related modification mechanism as a result of HCPEB irradiation was also investigated. After HCPEB post treatments, obvious changes in microstructure and significant hardening occur in the depth of 200-250 μm from the surface after HCPEB irradiation. Rapid heating and subsequent rapid solidification induce heavy plastic deformation, which results in that the laminated structure of pearlite is substituted by dispersive rounded-like cementites in the near-surface. The effect of HCPEB treatment can reach more than 500 m depth from the surface. The original crystalline structure is changed to a different degree that grows with the numbers of bombardment, and in the surface layer amorphous states and nanocrystaline structures consisting of grains of γ-phase and cementite are found. The violent stress induced by HCPEB irradiation is the origin of the nanostructured and amorphous structure formation.     

Surface modification of polyurethane and silicone for therapeutic medical technics by means of electron beam

Surface modification technologies are gaining growing acceptance for treatment of implant materials to enhance biocompatibility. Our examinations focus on polyetherurethane and silicones, two typical flexible implant materials, which we have modified by non-thermal electron beam processing. Advantages of this method are the adjustable degree of modification as well as the simultaneous sterilizing effects.The polymer surfaces were characterized with regard to wetting behavior, surface energy, chemistry and morphology. The cell adhesion was examined too. The results reveal that the electron beam is a useful tool for surface modification of polymers.     

Repair of EDM induced surface cracks by pulsed electron beam irradiation

This study investigates the use of the large-area electron beam irradiation technique to improve the properties of the EDM’d surface of AISI 310 stainless steel so that a tolerable, or even desirable recast layer may be produced. The short cycle-time of the irradiation process combined with the large incident area of 60 mm diameter makes it an attractive surface modification technique for metal moulds and engineering components. This study showed that by varying acceleration voltages and the number of irradiation cycles (shots), that as well as an improvement of surface finish, repair of cracks induced by the EDM process is possible. The mechanism of this repair is also investigated. XRD analysis also shows that crystalline texture can be introduced by the irradiation process with the (1 1 1) planes of the austenite phase orienting parallel to the surface. This has potential advantages for introducing anisotropic layers for enhanced corrosion resistance.     

316L不锈钢强流脉冲电子束表面钛合金化及其耐蚀性

利用强流脉冲电子束对不锈钢表面进行了快速钛合金化。将精细钛粉预涂在基体表面后采用强流脉冲电子束对其进行后处理。在电子束对表面的快速加热熔化、混合及增强扩散效应的作用下,部分钛熔入基体表层形成一层富钛层。由于钛的添加有利于形成α相,合金层由α相和γ相混合组成。在模拟体液中的动态极化测试表明,316L医用不锈钢经强流脉冲电子束表面钛合金化后,其在模拟体液中的耐腐蚀性能获得了显著的提高。     

Evolution of microstructure and non-equilibrium phases in electron beam treated Zr55Cu30Al10Ni5 bulk amorphous alloy

Electron beam (EB) is becoming very popular for the modification of the surfaces as it involves localized melting and fast cooling which helps in achieving the non-equilibrium phases as well as fine microstructure. Surface modification of Zr-based amorphous alloy Zr₅₅Cu₃₀Al₁₀Ni₅ has been carried out by EB melting. Differential scanning calorimetry (DSC) was employed to determine the supercooled liquid region and activation energy of crystallization. The as-cast and modified surfaces of amorphous alloy at different beam conditions were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. Various phases like NiZr₂, CuZr₂ and Cu₁₀Zr₇ were identified which resulted in the enhancement of hardness of the modified alloy surface.     

Surface roughness of a hot-dipped galvanized sheet steel as a function of deformation mode

A hot-dipped galvanized zinc-coated sheet steel was deformed with three different laboratory test systems: a Marciniak punch system, a flat-die friction test system, and a cupping system. These systems were able to impose various combinations of deformation modes to the sheet. The deformation modes include: (1) strain without die contact, (2) sliding, (3) pressing, and (4) bending. Strain measurements from the electrolitically gridded specimens were made at the same locations as surface profilometry measurements, allowing a direct correspondence of surface roughness with strain. Quantification of the roughening as a function of strain, sliding and bending was determined. The roughening rate depends upon the strain level as well as the strain path. Increased strain without die contact causes an increase in the surface roughness with strain paths close to plane strain exhibiting the highest roughening rate. The deformation modes of sliding, pressing, and bending cause a decrease in the surface roughness (i.e. smoothing) to occur. A first-order model is proposed to account for the surface roughness as a function of these deformation modes.     

Surface finishing of die and tool steels via plasma-based electron beam irradiation

The plasma-based electron beam (PBEB) irradiation with a maximum diameter of 60 mm has been used to smoothen the workpiece surface. After PBEB irradiation, the machined surface roughness is reduced, and its corrosion resistance is improved. However, for die and tool steels, some craters still exist on the surface after PBEB irradiation, which remain a big problem for the roughness improvement and quality control of the machined surfaces. In this study, four types of work materials have been tested during PBEB irradiation. The effects of non-metallic inclusions (MnS and carbide) and impurities on the generation of craters were investigated. In addition, craters formed on the work materials with different nitrogen concentrations have also been observed after PBEB irradiation. Finally, a case study is given, and it is found that PBEM irradiation can achieve good surface finish of die steel materials.     

Structure and hardness of titanium surfaces carburized by pulsed laser melting with graphite addition

Titanium foils coated with graphite films 20 μm thick were irradiated by means of a pulsed Nd-YAG in order to harden this metal by surface melting and alloying. The relationships between irradiation parameters, microstructure and hardness of the synthesized composite coatings were determined. Four relevant parameters were defined as governing the irradiation processes. The parametric working field of the laser source was investigated next to its periphery. The influences of the relevant irradiation parameters on the microstructure and hardness of the melted zone were deduced from the metallographic analyses and Vickers micro-indentation tests of the cross sections of this composite zone. Such a zone was constituted always with hard titanium carbide and ductile metallic titanium, some times with the presence of lubricating graphite inclusions. The main advantage of such a surface treatment of titanium is to synthesize, under clearly defined irradiation conditions, a self-lubricating composite coating that resists abrasive or adhesive wear.     

45钢电子束相变硬化温度场数值模拟与实验验证

建立了移动电子束高斯热源作用下的三维相变硬化过程中温度场的数学模型,分析过程中考虑了热源分布、热物性参数、热辐射等因素对温度场的影响,得到了电子束扫描相变硬化温度场的分布规律和硬化层的形态,并进行了实验验证;探讨了电子束工艺参数对硬化区深度和宽度的影响。结果表明:移动电子束高斯热源作用下的温度分布等值线呈勺状,表面最高温度滞后于束流中心,且处理后硬化层横截面呈月牙状;在固态相变条件下,硬化层的宽度和深度随着扫描功率的增加呈非线性增加,随着扫描速度的增加呈非线性减小。     

Surface modification of Al-Pb alloy by high current pulsed electron beam

Al-Pb alloy was modified by high current pulsed electron beam and the microstructure, hardness and tribological characteristics were characterized by scanning electron microscopy, electronic microanalysis probe microanalysis, Knoop hardness indentation and pin-on-disc type wear testing machine. The results show that the microstructure and hardness can be greatly improved, and the modification layer consists of a molten zone, an overlapped zone of heat-affected and quasistatic thermal stress-affected zone and a transition zone followed by the substrate. The tribological properties of high current pulsed electron beam irradiated Al-Pb alloy are correspondingly improved largely. Optical observation and scanning electron microscopy analysis reveal that the low wear rate and lowest level in coefficient of friction at high load level for irradiated Al-Pb alloy are due to the formation of a lubricious tribolayer covering the worn surface, which is a mixture of Al2O3, Pb3O4 and silicate. The wear mode varies from oxidative wear at low load to film spalling at high load and, finally, adhesive wear.     

Microstructure and fatigue crack growth behaviour of electron beam welding in 30CrMnSiNi2A steel

The effects of two post-weld heat treatment processes on the microstructure and fatigue properties of the electron beam welded joints of 30CrMnSiNi2A steel were studied. Electron beam local post-weld heat treatment ( EBLPWHT) , in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were accepted. The experimental results show that, after EBLPWHT, the main microstructure of weld is changed from coarse acicular martensite into lath martensite, and base metal is changed from ferrite and perlite into upper bainite and residual austenite, however the microstructures of different zones of joints in FWPWHT conditions are tempered sorbite. The fatigue crack growth rate da/dN of welds and base metal are not obviously changed among EBLPWHT, FWPWHT test and as-welded (AW) test, as the mechanical properties of materials have a certain but not large effect on the da/dN of welded joints. The resistance to near threshold fatigue crack growth data of welded joints can be largely improved by EBLPWHT and it is related to microstructure and crack closure effect.     

The model of formation of a non-self-sustained discharge in the plasma in electron beam welding

A model of formation of a non-self-sustained discharge in plasma in electron beam welding is proposed. The electron concentration and electron energy in the plasma above the zone of the effect of the electron beam are calculated by solving the convection–diffusion equations for the density and mean electron energy. Numerical calculations in the construction of the model are carried out using a package of applied software Comsol 4.3, the Plasma Module and the extension DC discharge. The model can be used to calculate the plasma parameters both above the welding zone and directly in the penetration channel.     

脉冲电子束改性TCA钛合金微观组织和性能

采用低能强电流(LEHC)脉冲改性技术处理TC4钛合金表面,利用扫描电子显微(SEM)、场发射扫描电镜(FESEM)、透射电子显微(TEM)和纳米压痕分析(NI)等方法对表面改性层组织进行表征,按照不同低能强电流脉冲改性工艺下改性层的组织特征,结合纳米压痕硬度试验,分析了脉冲电子束改性晶粒的细化机制。结果表明,脉冲电子束改性试样可分为熔化相变层、热影响层和基体三个区域;熔化相变层中的晶粒细化机制是脉冲电子束改性时随着温度的快速升高,表面层发生熔化后的重新结晶以及α相在β相中的析出;晶粒细化是表层纳米压痕硬度提高的主要原因。     

脉冲电子束抛光改性处理对TC21钛合金表面形貌的影响

采用脉冲电子束对TC21钛合金表面进行照射处理,利用光学显微镜、原子力显微镜分析了表面形貌,在轮廓仪上测定了脉冲电子束处理前后试样的表面粗糙度Ra和Ry,利用扫描电镜对脉冲电子束改性处理与未处理试样的横截面进行观察和分析,研究脉冲电子束改性机理.试验结果表明,脉冲电子束可以显著改善TC21钛合金的表面粗糙度,其抛光改性的机理是厚约10 μm表层在脉冲电子束的照射下发生高温瞬时熔凝,使表面变得平整和光滑.     

Mechanisms of nanostructure and metastable phase formations in the surface melted layers of a HCPEB-treated D2 steel

This work investigates the mechanism of surface modification associated with the high-current pulsed electron beam (HCPEB) treatment of a D2 steel with increasing numbers of pulses. The surface layers were melted and resolidified but the treated surfaces showed very different features. This variation is essentially due to the different levels of homogeneity and carbide dissolution. It is demonstrated that the presence of carbides served as nucleation sites for the surface eruption phenomenon that creates craters on the surface. After a sufficient number of pulses, most of the carbides in the surface layer were dissolved and an almost crater-free homogeneous melted layer consisting of a very stable nano-austenite structure was formed. The HCPEB technique is thus demonstrated to be a versatile technique for surface microstructure modification involving, in the case of steels, austenite stabilization and ultrafine grain formation.     

Effects of post-weld heat treatments on the residual stress and mechanical properties of electron beam welded sae 4130 steel plates

The distribution of the residual stresses of electron beam welded SAE 4130 and the effect of stress relief after various post- weld heat treatments (PWHT) were measured using X- ray diffraction. The mechanical properties and microstructure were also examined. Experimental results show that the tensile residual stress increased with the heat input of the electron beam. Most of the residual stresses were relieved by the PWHT at 530 °C for 2 h followed by furnace cooling to 50 °C. The strength of the welds decreased slightly, and the elongation of the welds increased after PWHT.     

不锈钢套管接头电子束钎焊的组织分析

确定了不锈钢管件套接接头电子束钎焊的工艺参数，并获得了良好的钎焊接头。利用扫描电镜和能谱分析仪，对电子束钎焊试样的显微组织进行了分析。结果表明，钎缝区主要是固溶体组织和少量的化合物；母材区除了奥氏体组织外，还存在Cu元素的晶闻扩散。