Characteristics of laser aided direct metal/material deposition process for tool steel

Laser aided direct metal/material deposition (DMD) process builds metallic parts layer-by-layer directly from the CAD representation. In general, the process uses powdered metal/materials fed into a melt-pool, creating fully dense parts. Success of this technology in the die and tool industry depends on the parts quality to be achieved. To obtain designed geometric dimensions and material properties, delicate control of the parameters such as laser power, spot diameter, traverse speed and powder mass flow rate is critical. In this paper, the dimensional and material characteristics of directed deposited H13 tool steel by CO₂ laser are investigated for the DMD process with a feedback height control system. The relationships between DMD process variables and the product characteristics are analyzed using statistical techniques. The performance of the DMD process is examined with the material characteristics of hardness, porosity, microstructure, and composition.     

Rapid prototyping of 4043 Al-alloy parts by cold metal transfer

The macro-structure, microstructure and mechanical properties of 4043 aluminium-alloy parts manufactured by variable polarity cold metal transfer welding (CMT?+?Advance) have been investigated. The results showed that processing parameters have a strong effect on the geometry, microstructures, roughness and hardness of a deposited part. The problem of the hump and arc collapse was solved by the adjustment of specific welding parameters. Different morphologies were formed at different locations according to the observation of the microstructure. The elemental segregation was found between the layers of the component. The results showed that the dimensional accuracy of the single wall forming sample could be controlled much better by means of adjusting the parameters and optimising the path, thus excellent sample would be obtained.     

Deposition of Ti-6Al-4V using a high power diode laser and wire, Part II: Investigation on the mechanical properties

The deposition with high power diode laser and Ti6Al4V wire was verified as a process which can provide a high deposition rate with good quality. Sound mechanical properties of the deposited parts are the prerequisites for the real applications of this process. In this paper, the main mechanical properties including micro-hardness and tensile properties were investigated. Single bead walls were deposited. Test pieces were machined from the deposited walls according to the British standard for the mechanical tests.The epitaxial columnar grains were found growing parallel to the building direction. A band region was observed between two deposited layers, which resulted from the remelting of previously deposited layer and multiple thermal cycles that had occurred with each subsequent deposition pass. The results showed that with the same laser power, the built samples with higher traverse speed possess similar or slightly higher hardness than the samples built with lower traverse speed. The hardness varied less than 10% with different sets of parameters. The investigations on the tensile properties were carried out with the samples as deposited and stress relieved at 700 °C in an air circulating furnace for 2 h. The as deposited samples showed better tensile properties than the stress relieved ones. This results from the reduction of the compressive residual stresses and the coarser microstructure after stress relief. The tensile properties also showed dependence on the direction of the test carried out. All the examined tensile properties of the as deposited samples matched properties of the as cast and wrought material.     

渗氮温度对42CrMo钢零件表面后氧化渗层的影响

采用硬度测试、显微组织观察、脆性等级和疏松等级评价等方法研究了渗氮温度对42CrMo钢零件渗氮后氧化渗层性能的影响。结果表明:在渗氮后氧化处理过程中,渗层的表面硬度随着渗氮温度的升高出现先增后降的趋势;渗层深度和疏松等级随渗氮温度的升高而增加,但脆性等级变化不大。当渗氮温度为560 ℃时,42CrMo钢零件可获得表面硬度≥600 HV、渗层(白亮层)深度≥15 μm、1级脆性等级、2级疏松等级的优秀渗层。     

Influences of ceria and yttrium on properties of D127 surfacing electrode

The coating of D127,a surfacing electrode,was added ceria(CeO_2) and yttrium (Y) for possible enhanced electrode properties.The method of orthogonal test was adopted.The coating with different amount of CeO_2 and Y was pressed.The hardness of surfacing layer was carried on by hardness tester,microstructure was investigated by metallograph,and the content of rare earths was analyzed by X-ray energy dispersive spectrometer.The results show that the microstructures of deposited metal can be effectively made fine,accordingly,the hardness and the wear-resistance of deposited metal are also raised.But the addition amount of the rare-earth should be proper.The deposited metal microstructure is the finest and the most homogeneous when the addition amount of CeO_2 is 2 wt.% and Y 1.2 wt.%,and the hardness of the surfacing layer is the highest.     

Magnetic NDT Technology for characterization of decarburizing depth

From practical point of view, determining the decarburizing depth is important in quality control of steel parts as it has undesirable effects on the mechanical properties such as hardness, wear and fatigue resistance. Traditional destructive methods of determining the depth of decarburized layer include metallographic and hardness test which are time-consuming and costly. Since response to eddy current is sensitive to chemical composition as well as microstructure of the material under consideration, the non-destructive method can be used in determining the depth of the decarburized layer in steel parts. It is mainly due to the difference in the microstructures, and as a result, in the magnetic properties of the decarburized layer with other parts of the specimen. In the present study at the first step, the magnetic properties of decarburized carbon steel bars (0.45 wt.% C) were evaluated using an electromagnetic sensor and correlated with the microstructure changes from surface to the core of the sample. At the second step the steel bars were held in 900 °C for different period of times and the depth of decarburizing layers were measured using hardness testing. Finally, the non-destructive eddy current technique was used and the response of test samples to the induction current including primary and secondary voltages, normalized impedance, phase angle and harmonic analysis parameters were investigated. Results show an acceptable accuracy in comparison to the destructive method.     

低频磁场对堆焊层组织及耐磨性的影响

通过对低频纵向磁场作用下埋弧堆焊焊缝成形、硬度、耐磨性及微观组织分析,研究了低频磁场对熔敷金属的组织和力学性能的影响规律,探讨了低频磁场改善熔敷金属组织形态、提高堆焊层耐磨性的机理.试验发现,加低频纵向磁场后焊缝的熔宽增加,熔深略有减少;晶粒尺寸由25.6μm降低到10.6 μn,硬度由50.5HRC提高到55.0HR...     

航空不锈钢1Cr11Ni2W2MoV精密薄层气体氮碳共渗

对航空不锈钢1Cr11Ni2W2MoV进行气体氮碳共渗热处理,以获得深度为0.02～0.03 mm的精密薄层,并对不同工艺参数下的渗层深度、硬度和脆性、组织进行了检测和分析。结果表明,在480～560℃共渗温度下,通过控制保温时间,均可得到深度0.02～0.03 mm,硬度≥800 HV0.1的精密渗层。温度越高,保温时间越长,渗层厚度和硬度越大。从工艺控制稳定性和生产效率等方面考虑,520℃温度下渗入速率均匀易控,更适合零件的实际生产。所得渗层脆性达到HB 5022—1994中1～2级的要求,组织符合2级及以上要求。     

45钢表面电子束微熔抛光的性能和组织分析

为显著改善45钢表面粗糙度及其综合力学性能. 文中采用电子束微熔抛光技术,对45钢表面进行电子束微熔抛光处理. 研究电子束抛光对表面粗糙度、改性层组织和硬度的影响,探讨了电子束扫描电流、扫描速度对表面粗糙度、改性层组织的影响规律. 结果表明,45钢经表面抛光处理后,表面粗糙度值由2.091 μm降到0.738 μm,降幅为64.7%;其表面改性层可分为抛光层区、热影响区和基体区;抛光层区的显微组织为针状马氏体,硬度为950 ~ 913 HV;热影响区的组织为针状马氏体和铁素体,硬度为855 ~ 280 HV;基体区的组织为珠光体和铁素体,硬度为244 ~ 204 HV. 电子束工艺参数对抛光后的表面粗糙度值影响显著,在满足抛光效果的条件下,改性层的厚度随电子束扫描电流的增加而增大,随扫描速度的增加而减小.     

基于BC-MIG焊的铝/钢异种金属增材制造工艺

以2 mm厚Q235镀锌钢板为基板,直径1.2 mm的4043铝合金焊丝为增材材料,利用BC-MIG焊工艺进行增材试验,得到了成形美观,性能优良的T型材结构. 采用金相显微镜、显微硬度仪、万能拉伸试验机对接头的组织形貌、硬度分布、剪切性能进行研究,获得了沉积层的组织和力学性能的变化规律. 结果表明,沉积层最底部靠铝一侧和靠钢一侧分别形成细长针状和带状Fe/Al化合物,沉积层中部由向上生长的树枝晶组成,而在沉积层顶部的组织没有定向生长的趋势. 剪切试验表明,铝/钢异种金属T型材最大可承受2 108 N的剪切力,剪切角达到13.5°时,受力一侧堆焊层根部发生断裂,堆焊层上无明显裂纹.     

Deposition of Ti-6Al-4V using laser and wire, part II: Hardness and dimensions of single beads

Mechanical properties of additive manufactured components are greatly dependent on the microstructure, which is in turn greatly dependent on the thermal history. Single beads deposited are the fundamental unit of multi-layered components manufactured by an additive process. Dimensions and hardness of numerous single beads deposited and bead-on-plates are measured. The results are evaluated statistically in terms of indicating thermal history. The beads were produced using a Nd:YAG laser, Ti-6Al-4V substrate and Ti-6Al-4V (extra low interstitials) wire. The parameters varied are the laser beam power, welding speed, and wire-feed speed. The experiments show that hardness measurements are not necessarily useful to indicate thermal history, in contrast to dimensional measurements.     

CHR焊条堆焊金属显微组织与显微硬度分析

采用焊条电弧堆焊技术,以不同的焊接工艺参数,选用堆焊焊条CHR132在45#钢基体上进行多层堆焊试验.采用光学显微镜观察分析了堆焊金属显微组织,利用硬度测试仪测试了堆焊金属的硬度,讨论了焊接线能量对堆焊层金属显微组织的形成、硬度的影响.研究结果表明:堆焊金属的显微组织和显微硬度不仅与堆焊工艺参数有关,且与硬质相的类型、性能、数量、分布等有关.     

热处理对GTA增材制造TiAl合金组织与性能的调控

针对Al原子含量为45%的电弧沉积态TiAl合金,进行了基于热处理的组织与性能调控研究. 结合Ti-Al二元相图分别制定了1080, 1200, 1270, 1350 ℃ 4个加热温度,保温1 h后随炉冷却. 结果表明,随着加热温度的升高,合金内偏析现象逐渐消失,晶界γ相减少,组织形态逐渐向全层片结构转变,且层片晶团尺寸逐渐增加. 在1350 ℃下分别保温5,30 min和1 h,发现随着保温时间的延长,层片晶团逐渐粗化. 基于单级热处理试验结果提出循环热处理工艺,将沉积态合金在900 ~ 1200 ℃之间多次循环“加热-短时保温-冷却”,获得了细小的层片晶团组织,合金硬度降低,抗压强度与压缩率均提高.     

Influence of Powder Morphology and Microstructure on the Cold Spray and Mechanical Properties of Ti6Al4V Coatings

The powder microstructure and morphology has significant influence on the cold sprayability of Ti6Al4V coatings. Here, we compare the cold sprayability and properties of coatings obtained from Ti6Al4V powders of spherical morphology (SM) manufactured using plasma gas atomization and irregular morphology (IM) manufactured using the Armstrong process. Coatings deposited using IM powders had negligible porosity and better properties compared to coatings deposited using SM powders due to higher particle impact velocities, porous surface morphology and more deformable microstructure. To evaluate the cohesive strength, multi-scale indentation was performed and hardness loss parameter was calculated. Coatings deposited using SM powders exhibited poor cohesive strength compared to coatings deposited using IM powders. Images of the residual indents showed de-bonding and sliding of adjacent splats in the coatings deposited using SM powders irrespective of the load. Coatings deposited using IM powders showed no evidence of de-bonding at low loads. At high loads, splat de-bonding was observed resulting in hardness loss despite negligible porosity. Thus, while the powders from Armstrong process lead to a significant improvement in sprayability and coating properties, further optimization of powder and cold spray process will be required as well as consideration of post-annealing treatments to obtain acceptable cohesive strength.     

基于SLM技术对H13钢性能的研究

基于SLM技术,探究激光功率、扫描速度、铺粉厚度3个工艺参数对H13钢成型性能的影响程度,采用L9(33)的正交试验方案,并对试验数据进行极差、方差分析以及相关性检验,得到了工艺参数对尺寸精度、硬度、表面粗糙度、冲击韧性以及在同权重情况下试样综合性能的影响。试验结果表明,铺粉厚度对硬度、尺寸精度、综合性能的影响最大;扫描速度对表面粗糙度、冲击韧性影响最大;激光功率对表面粗糙度、尺寸精度、综合性能的影响介于二者之间,对硬度、冲击韧性的影响程度最小;铺粉厚度与尺寸精度、综合性能有较强的负线性关系。     

42CrMo钢阀杆断裂失效分析

42CrMo钢阀杆在使用过程中倒角部因承受较大的力而发生断裂。采用金相显微镜和扫描电镜对液压件渗碳表层及过渡层的组织特征进行分析，用显微硬度计测定阀杆硬化层深度和硬度梯度分布，从组织结构和硬度分布分析失效原因。结果显示，阀杆的强度和硬度都低于技术条件要求，阀杆的结构设计以及硬度和强度降低是阀杆断裂的最主要原因。     

铌含量对Fe-C-Cr-Nb系表面熔覆金属组织及耐磨性的影响

目的 提高钢表面熔覆层的硬度、耐磨性及其综合性能。方法 运用气体保护焊堆焊不同Nb含量的Fe-C-Cr-Nb系表面堆焊材料,采用JmatPro软件模拟计算不同铌含量的熔覆层CCT曲线和平衡冷区曲线,分析铌含量对熔覆组织转变和析出相的影响。运用光学显微镜、扫描电镜和X射线衍射仪观察晶粒尺寸和熔覆组织形貌,并对析出相进行分析。利用洛氏硬度计和滑动摩擦磨损试验机,分别对熔覆金属进行宏观硬度和耐磨性的测定。结果 不同铌含量熔覆组织均由马氏体和少量贝氏体组成,基体有大量的MC型碳化物析出。当Nb含量为1.5%时,碳化物弥散分布在熔覆组织中,强化效果最佳,此时硬度最高,为55.3HRC。此外,MC型碳化物有明显的细化晶粒作用,显著提高了熔覆组织的韧性。硬质相与韧性基体的配合,使熔覆组织的耐磨性在铌含量为1.5%时达到最佳。结论 通过调整Fe-C-Cr-Nb系表面堆焊材料中铌的含量,可以有效地控制熔覆金属组织类型及碳化物组成和分布,从而提高熔覆层的综合性能。     

微束等离子弧粉末熔覆金属成形件的组织及性能

采用微束等离子弧粉末熔覆技术在Q235低碳钢基板上利用铁基合金粉末Fe313直接金属成形筒状零件毛坯.通过金相显微镜、扫描电镜观察成形金属零件显微组织和形貌,进行EDS分析,并测试了熔覆层的显微硬度.结果表明,等离子弧粉末熔覆直接成形工件的显微组织受到后续成形工艺循环加热的影响而晶粒细化,成形工件硬度沿高度呈U形分布.     

电火花沉积工艺及沉积层性能的研究

为了研究电火花沉积工艺对沉积层组织结构及沉积层性能的影响,改善电火花沉积层的表面质量.采用新型电火花沉积设备,以YG8电极材料,H13(4Cr5MoSiV)钢为基体材料进行了沉积实验.通过工艺实验,研究了沉积时间、沉积功率、沉积电压、沉积频率和沉积气氛对沉积层的影响规律,用X射线衍射仪分析了沉积层的组织结构,通过硬度实验和抗磨损实验测定了沉积层的纤维硬度和抗磨损性能.试验表明,电火花沉积工艺对沉积层的组织结构和沉积层性能有影响,沉积层内的白亮层含有大量复杂化合物,具有高的纤维硬度和高的耐磨性.     

Evaluation of the mechanical properties of Inconel 718 components built by laser cladding

Laser-cladding process is one of the most relevant new processes in the industry due to the particular properties of the processed parts. The main users of this process are aeronautical turbine parts manufacturers and engineering maintenance services. The main advantage of laser-cladding process is the possibility of obtaining high quality material deposition on complex parts. Thus, laser cladding can be applied in the repair of high added-value and safety critical parts. This ability is especially useful for high-cost parts that present wears or local damage due to operating conditions. Different types of parts can be processed, such as housings, blades or even complete turbine rotors. Once the parts are repaired by laser cladding, they can be reassembled on the engine, reducing lead times. Laser-cladding process can permit buildup of complex geometries on previously forged or machined parts, such as stubs or flanges.However, one of the main drawbacks of the laser-cladding process currently is lack of knowledge on the properties of the deposited material. Most of the available data relate to the microstructure and the final hardness values. Nevertheless, there are few data of the mechanical properties of the parts. Moreover, it is difficult to gather data related to the influence of the laser-cladding parameters and strategies on the mechanical behaviour of a part.This paper presents the mechanical properties of a series of samples builtup by laser cladding. Two different types of specimens are tested: first, hybrid parts, in which laser cladding deposits materials built up layer-by-layer onto a substrate and the resulting part is a combination of deposited material and the substrate and second, complete rapid manufactured test samples. The results of tensile tests on various parts show that the laser-cladding strategy has a significant influence on their stress-strain curves. In addition, the laser-cladding process can result in a high directionality of their mechanical properties. The direction depends on the particular strategy in use. The study demonstrates that these properties present high anisotropy, a factor that should be carefully considered when selecting the most appropriate laser-cladding strategy.