Improving the Fatigue Strength of Laser Powder Bed-Fused AISI M3:2 by Hot Isostatic Pressing

Laser additive manufacturing enables the one-step fabrication of complex parts. However, pores and carbide networks, which are not avoidable from the laser powder-bed fusion (LPBF) process, deteriorate the fatigue strength significantly. Hot isostatic pressing (HIP) with integrated heat treatment is a powerful post-treatment that densifies the material and modifies the microstructure. Herein, AISI M3:2 samples are produced by LPBF and then are either austenitized, quenched, and tempered in a HIP unit under pressure or are only hardened and tempered in a vacuum oven. The corresponding microstructure is analyzed by optical microscopy, scanning electron microscopy using energy-dispersive X-ray spectroscopy, and X-ray diffraction. The fatigue strength is determined by rotation bending tests. Fracture surfaces are observed under scanning electron microscopy for failure analysis. While both post-treatments lead to similar microstructure, the fatigue strength is significantly improved by the HIP process.     

Effect of subsequent Hot Isostatic Pressing on mechanical properties of ASTM F75 alloy produced by Selective Laser Melting

Abstract

The Co-based alloy ASTM (Co – 28.5?wt.-% Cr – 6.3?wt.-% Mo) is widely used for medical implants, e.g. knee prostheses, and is commonly processed by investment casting. Selective laser (SLM) melting is supposed to be an efficient alternative for the production of individually designed knee implants regarding production time and production costs. The mechanical properties, in particular the fatigue strength, of the material have been studied in different states of the material. The mechanical properties of investment casted ASTM F75 and PM-SLM produced ASTM F75 were investigated. The focus in this study was on the PM-SLM material, the specimens were initially produced by selective laser melting and a part of the specimens were further processed by hot isostatic pressing (HIP). The PM-SLM material was mechanically tested in the as-SLM state as well as in the SLM+HIP state. It was found that the mechanical properties of the as-SLM material did not reach the level of the fatigue strength of as cast material. The post-densification treatment by HIP offers distinct improvements regarding the fatigue strength compared to the as-SLM material.     

大尺寸亚微米硬质合金顶锤的热等静压研制

以超细晶WC-Co喷雾干燥混合粉为原料,通过成形、脱蜡、真空烧结和热等静压(HIP)等工序制备出?160 mm以上的大尺寸YG10X亚微米硬质合金顶锤。研究了真空烧结与HIP处理相匹配工艺,以及不同脱蜡气氛对顶锤组织和性能的影响。采用200～300℃×40 h缓慢的氢气连续脱蜡、匹配的烧结工艺辅以1 380℃热等静压制得的?188 mm顶锤,其组织均匀,晶粒细小,性能稳定,各部位横向断裂强度均高于4 100 MPa,顶锤平均使用寿命在9 000～11 500次以上。     

真空感应熔炼AerMet100超高强度钢脱氮实验研究

摘要：通过取样检测并结合热力学和动力学计算研究了氧化镁质（MgO）、镁铝尖晶石质（MgO·Al2O3）和氧化钙质（CaO）3种坩埚和2种真空压力（50~100Pa和5~10Pa）对AerMet100超高强度钢脱氮的影响。实验结果表明：随着精炼时间增加,3种坩埚在2种真空压力下的钢液中N质量分数都逐渐减少。相比之下,CaO坩埚脱氮效果最佳,2种真空压力下30min时N质量分数均减少到0.0005%。动力学计算结果表明：MgO和MgO·Al2O3坩埚在2种真空压力下的钢液中O和S活度较高,脱氮反应均服从2级,即钢液脱氮受界面化学反应控制;而CaO坩埚在2种真空压力下的钢液中O和S活度较低,脱氮反应均服从1~5级,即钢液脱氮由液相边界层传质和界面化学反应共同控制。此外,减小真空压力,脱氮速率加快,有利于钢液脱氮。     

等静压成型工艺参数对高纯石墨制品的影响研究

实验研究了高纯石墨材料制备过程中,等静压成型工艺参数对制品的影响.研究了升、降压速度,等静压压力及保压时间、包套长径比对压坯体积密度的影响.结果表明,降低升压速度、增加等静压压力有利于提高制品密度,适当的降压速度、保压时间和包套长径比可使压坯致密均匀.     

热轧H型钢的高应变低周疲劳性能研究

 对热轧H型钢的高应变低周疲劳性能进行了研究。采用轴向应变控制的方法，在Instron-1342型电液伺服疲劳试验机上测定了热轧H型钢的低周疲劳性能数据，研究了在循环载荷下材料的循环应力响应特征、循环应力与应变关系，并用Coffin-Manson公式拟合得到热轧H型钢的疲劳寿命计算公式，据此计算了 =100时的 值。通过断口扫描发现，裂纹不仅在试样表面处形核，同时也在试样内部杂质处形核，然后通过不断的扩展形成微裂纹，许多微裂纹通过扩展连接形成宏观裂纹，最终导致材料断裂。     

二次硬化超高强度钢的高周疲劳性能研究

研究了采用真空感应+真空自耗重熔工艺冶炼的高纯净二次硬化超高强度AF1410钢的高周疲劳和疲劳裂纹扩展性能.结果表明:高纯净度AF1410钢具有优异的强韧性配合和较高的抗疲劳裂纹扩展能力,应力比尺为0.1时,其光滑(Kt=1)和缺口(Kt=3)疲劳强度分别为1 375MPa和417MPa,且疲劳裂纹源均起始于试样表面缺...     

Fatigue Behavior of High Speed Steel Roll Materials for Hot Rolling by Laser Impacting

The fatigue behavior of high speed steel （HSS） roll materials for hot rolling was researched under watercooling conditions by laser impacting. The microstructure of HSS sample and the morphologies of fatigue samples were observed by scanning electron microscope. The phase structure was detected by XRD. The morphology of situ oxide scale was observed by optical microscope, and the expansion coefficient was measured by TGA. The experiment results indicate that the cracks come into being at the carbide-matrix interface, but there are no cracks in the matrix after many times of laser impacting treatment, for the situ sample taken from the fractured roll surface, big carbides are more sensitive to the fatigue, and peel off prior to small ones. The relevant fatigue mechanisms are also discussed.     

Tailoring of Mechanical Properties of Indirect Hot Stamping Steel Tubes by Laser Assisted Local Rapid Heating

The effect of laser assisted local heating on the mechanical properties of a hot stamping steel tube was in-vestigated.A heated region with a spiral shape was generated on the surface of the tube by combining the linear movement of the laser and the rotation of the tube.The results of axial crush tests show that the laser assisted local heating can be effectively used to modify the mechanical performance of the tube.A microstructural analysis confirms that the laser locally induces a martensitic phase transformation in the heated region and results in inhomogeneous microstructures along the length of the tube.     

Fatigue Properties of Laser Hybrid Weldments on Structural Steel

The behaviour of laser hybrid weldments under cyclic load was examined. The laser hybrid butt joints made of high‐strength steel S690Q and structural steel EH36 (S355) were investigated in 4‐point bending tests. The S‐N lines were established for 15, 20 and 25 mm thick specimens. The weldments were manufactured in two variants: without a gap between the connected plates and with a narrow gap between them. The calculations were carried out in accordance with IIW and EC3 recommendations. The influence of defects on fatigue resistance was estimated in additional tests using samples with weld defects, which were determined by X‐ray methods.     

两种不同冶金工艺生产的60Si2CrVA弹簧钢的高周疲劳性能

 采用旋转弯曲疲劳试验研究了两种不同冶金工艺生产的60Si2CrVA弹簧钢的高周疲劳破坏行为。结果表明,尽管两种试验料的氧含量接近,但两者夹杂物特征的差异使其疲劳性能存在明显的差异。与采用电炉+LF+VD+CC工艺生产的X8料相比,采用转炉＋LF+RH+CC工艺生产的X6料中的夹杂物数量明显减少,夹杂物尺寸较小,同时还减少了不规则的多棱角富Al2O3夹杂,因而后者的疲劳强度得到明显提高,并具有良好的疲劳寿命稳定性。     

Thermal Fatigue Behavior of AISI H13 Hot Work Tool Steel Produced by Direct Laser Metal Deposition

Direct laser metal deposition (DLMD) is an additive manufacturing technique getting growing attention thanks to the possibility of producing very complex parts in a short time and in a cost-effective manner. The possible applications of this technology are tools with conformal cooling channels and claddings for dies and molds reparation. One of the damaging mechanisms of tools is thermal fatigue (TF) cracking, leading to surface deterioration and, consequently, the processed parts. Herein, the TF behavior of DLMD-H13 submitted to two different heat treatments, namely direct tempering (T) and quenching and tempering (QT), is investigated. T does not significantly change the solidification microstructure after DLMD, whereas QT produces a more homogenous tempered martensite microstructure. A customary laboratory test is developed to induce TF damage under a cyclic temperature variation between 630 and 60 °C. The results evidence that the T-H13 has a slightly better TF resistance with respect to QT-H13 due to the higher tempering resistance of T-H13 with respect to QT-H13. Thus, according to TF test results, direct tempering can be preferred to quench and tempering since the elimination of quenching can decrease the costs of production as well as distortions-related issues, increasing the competitiveness of DLMD.     

热变形对中铬半钢热疲劳裂纹扩展动力学的影响

研究了热变形对中铬半钢热疲劳裂纹扩展动力学的影响。结果表明 :中铬半钢的热疲劳裂纹扩展符合 L =b Na(a<1)的关系。变形量小于 4 0 %时 ,随变形量的增加 ,裂纹扩展速率减小 ,其激活能随之增大。这些变化是由于碳化物形状的改变和粒状碳化物的析出所致。     

Effects of mechanical properties on precipitation hardening stainless steel by selective laser melting,hot isostatic pressing,solid-solution and aging treatments

ABSTRACT

The selective laser melting (SLM) process has gained considerable attention from industry and academia over the recent years. Furthermore, the hot isostatic pressing (HIP) technique has been widely applied as a post-treatment to increase the relative density of the fabricated parts. The main aim of this study is to investigate the effects of porosity elimination and mechanical properties on precipitation hardening stainless steel using SLM, HIP, solid-solution and aging treatments. This study also applied various laser scanning pitches (170, 210 and 250?μm), so that a significant phase transformation occurred between the SLM, HIP, solid-solution and aging treatments. The results showed that the laser scanning pitch was 170?μm, and after HIP, solid-solution and aging treatments the materials possessed optimal mechanical properties. The highest hardness (48.8?±?0.5 HRC) and TRS (2247.0?±?157.8?MPa) could be acquired.     

Effect of Hot Pressing on Microstructure and Mechanical Properties of Bulk Nanocrystalline Fe3Al Materials Containing Manganese Element

 Bulk nanocrystalline Fe3Al materials containing manganese of 10% were prepared by aluminothermic reaction. Hot pressing of those materials was performed at different temperatures and times. The microstructures of the alloy were investigated by optical microscope (OM) and electron probe microanalyzer (EPMA). The grain sizes of the materials were analyzed by X-ray diffraction (XRD) and transmission electron microscope (TEM). The results showed that the grain sizes of the materials increase after hot pressing. The grain sizes of the materials decrease with increasing the hot pressing times at the same temperature and the grain sizes of the materials increase with increasing hot pressing temperatures at identical times. The hardness and compressibility of the materials were also tested. The results showed that the hardness decreases with increasing hot pressing times at 800 ℃ and hardness increases with increasing the hot pressing temperatures. The variation of hardness with grain size of the nanocrystalline Fe3Al materials after hot pressing is contrary to the Hall-Petch relation. The materials are not broken during hot pressing and exhibit good plasticity and compressibility.     

热压工艺对SiC纤维增强TB8复合材料组织影响研究

通过箔-纤维-箔法制备了SiC纤维增强TB8复合材料,采用光学电子显微镜(OM)、扫描电镜(SEM)和电子探针(EPMA)对复合材料的微观组织进行表征与分析,研究了真空热压复合时压力、温度和时间工艺参数对SiC纤维增强TB8复合材料微观组织的影响规律。结果表明:压力对复合材料基体与基体以及纤维与基体的结合有着显著影响,而温度对纤维与基体界面反应层影响较大。通过热压工艺的优化,可以有效控制界面反应层厚度,获得组织优良的SiC f/TB8复合材料。     

镧对5CrMnMo热作模具钢力学性能的影响

研究了La对5CrMnMo钢的强度、硬度、塑性和冲击韧性的影响,并在相同的热处理工艺条件下,分别加入3种不同含量La后与不添加La的5CrMnMo钢的力学性能进行对比。结果表明：La加入量在适当的范围内可显著提高5CrMnMo的强度、硬度、塑性和冲击韧性,并且当La加入量为0.25%（质量分数）时,5CrMnMo钢可获得最好的综合力学性能。