选区激光熔化制备颗粒增强金属基复合材料的研究进展

选区激光熔化是一种使用聚焦高能激光束熔化粉末,逐层叠加成形零件的增材制造方法.选区激光熔化可以直接制备复杂结构零件和实现近净成形,能够方便地通过粉末预混添加或原位反应实现颗粒增强金属基复合材料的控形控性,具有独特的技术优势,受到广泛关注.本文综述了选区激光熔化制备颗粒增强金属基复合材料的研究进展,总结了主要研究结果及存在的共性问题,并展望了选区激光熔化制备颗粒增强金属基复合材料的研究方向和发展趋势.通过总结分析,指出选区激光熔化制备颗粒增强金属基复合材料时,聚焦激光作用下形成的高温微小熔池凝固时间短,远远偏离平衡状态,凝固过程复杂,增强颗粒与基体间冶金反应剧烈,容易熔化、分解和溶解并对基体特性产生影响,进而影响成形后的复合材料的宏观形貌和组织、性能.除增强体成分、颗粒形貌与尺寸、体积分数外,复合材料的性能还受激光功率、扫描速度、扫描间距、粉层厚度、成形气氛等工艺参数的影响,粉末特性与工艺参数之间的交互作用复杂.因此,考察工艺参数与粉末特性之间的交互作用关系,系统研究增强体颗粒特性与成形工艺参数对复合材料宏观形貌、致密度、缺陷、组织和性能的影响规律,是实现复合材料组织结构设计和性能调控的基础.     

激光重熔改性对电弧喷涂Al涂层性能的影响

为改进电弧喷涂Al层和钢基体之间的结合强度,利用Comsol软件分析不同激光功率对材料温度场的影响,然后通过激光重熔工艺对模拟结果进行实验验证。采用扫描电子显微镜(SEM)、能谱仪(EDS)分析试样界面形貌、涂层化学元素与微观结构组成,探讨了涂层与基体的结合性能,并通过电化学腐蚀实验分析涂层耐腐蚀性能。结果表明,在600W和1000W激光功率下,基体与涂层均未实现理想结合;在800W功率下,Al涂层与基体在激光重熔后由机械结合变为冶金结合,形成了基体-结合层-涂层的复合结构,使基体与涂层的结合性能得到显著提高,强化了Al涂层的耐腐蚀性能。     

轮轨试样Co基合金激光熔覆层组织及磨损性能

为提高轮轨材料的耐磨性降低轮轨磨损,利用CO2多模激光器在轮轨试样表面获得Co基合金熔覆层,测试分析了其组织结构性能和显微硬度,利用MMS-2A微机控制摩擦磨损试验机对比研究了激光熔覆处理与未处理轮轨试样的抗磨损性能.结果表明:激光熔覆处理后在轮轨试样表面获得与基体良好结合厚度约1 mm的熔覆层;熔覆层主要由枝晶(γ-Co)和共晶组织(Cr23C6+γ-Co)构成,初生相为γ-Co过饱和固溶体,富含Cr元素,共晶组织中富含Co元素;结合区为粗大柱状晶,从中部到表层出现胞状晶、树枝晶等多种形态.离界面越远组织越细密,组织生长方向紊乱;结合区存在元素扩散,尤其是Fe、Cr和Co含量变化显著;激光熔覆Co基合金后轮轨试样硬度分别提高约52.98%和43.44%,能有效降低对摩副磨损,轮轨抗磨损能力提高约为原来的5倍.     

激光功率对PLC控制的SLM成形SiC增强铝基复合材料组织与性能的影响

目的 提升激光选区熔化成形(SLM)SiC增强铝基复合材料的力学性能。方法 以球形纳米SiC和类球形AlSi10Mg粉末为原料,采用球磨工艺和基于PLC控制的SLM技术制备了SiC增强铝基复合材料(SiC/AlSi10Mg),考察了激光功率对复合材料物相、显微组织和力学性能的影响。结果 复合粉末和激光功率为120~240 W的复合材料都主要含Al相和Si相;随着激光功率的增大,Al相择优结晶取向由(111)晶面转变到(200)晶面,在较高激光功率下,SLM成形试样中SiC熔化并与基体材料发生反应形成了Al4SiC4、Al4C3碳化物。在不同激光功率的SLM成形复合材料中都可见暗黑色α-Al基体和灰白色Al-Si共晶;随着激光功率增至210 W,Al-Si共晶组织逐渐碎片化并演变为网状,平均晶粒尺寸和小角度晶界体积分数逐渐增大。当激光功率从150 W增至240 W时,复合材料的纳米硬度和弹性模量先增后减,压缩强度逐渐减小,抗拉强度逐渐增大、断后伸长率先减后增而后又减小。结论 当激光功率为210 W时,SiC增强铝基复合材料具有良好的综合力学性能,这主要与组织均匀化、晶粒细化以及碳化物/基体界面结合改善等有关。     

直接金属粉末激光烧结成形机制的研究

分析了直接金属粉末激光烧结中单组元金属粉末、多组元金属粉末和预合金粉末的烧结成形机制;详细讨论了表面张力、粘度、颗粒尺寸及其分布和吸收率/反射率等材料特性以及激光参数、铺粉厚度、保护气氛、粉床预热温度和烧结辅助材料等工艺参数对成形质量的影响;并讨论了直接金属粉末激光烧结的进一步研究方向.     

激光熔覆沉积钛基复合材料的组织及性能

通过在激光熔覆沉积过程中向熔池内送入一定比例纯Ti粉和B4C颗粒，直接制备出钛基复合材料，分析了所制备材料的微观组织、相组成及性能。结果表明，在激光熔覆沉积过程中，Ti粉和B4C颗粒发生原位反应，生成与基体界面结合良好的TiC和TiB增强相，TiC为短棒状或颗粒状，TiB为短纤维状，复合材料中同时有大量未完全反应的B4C颗粒存在，所制备钛基复合材料的抗拉强度、硬度较激光熔覆沉积的纯钛有较大幅度的提高。     

45钢表面Ni基激光熔覆层的耐蚀性能

为改善45钢表面的力学性能和耐蚀性,在相同功率下采用不同扫描速率在其表面激光熔覆制备了Ni基(Ni35A)复合涂层。利用金相显微镜、X射线衍射仪、显微硬度计和电化学腐蚀测试系统对熔覆试样进行组织形貌、相组成、显微硬度和耐蚀性能分析。结果表明:熔覆试样由熔覆层、结合区和基体3部分组成;熔覆层组织细密并与基体冶金结合,扫描速率过大时易形成裂纹;熔覆层主要由FeNi3和Ni3B相组成,不同速率所得熔覆层显微硬度均超过400 HV;扫描速率为500 mm/min时熔覆试样自腐蚀电位提高了40 mV。     

送粉式激光熔覆基础理论研究

首次提出并实验证明了送粉激光熔覆过程中,熔覆材料与基材表面同时被激光加热的观点。首次提出了激光热有效利用率、透光率、吸收透光能量线密度、有效送粉系数、局部稀释率等基本概念,并给出相应参数的实验检测方法,且成功地对其进行实验检测。首次建立了:①不同条件下熔覆材料颗粒半径与工艺参数、材料物理性能之间的关系式;②透光率计算数学模型;③理论吸收透光能量线密度P_m计算模型;④显微组织分析法检测透光率估算公式;⑤基体表面单位时间内吸收热量计算模型。首次发现有效送粉系数随扫描速度增大出现极大值现象是由熔覆材料加热温度和送粉器喷嘴宽度与激光束动直径的大小决定的。当两者尺寸相当时,熔覆材料粉将得到最充分的利用。首次提出用熔覆层界面附近硬度梯度曲线及拐点连线分析研究熔履层界面附近真实稀释率。首次提出送粉激光熔覆过程中熔覆材料与熔化的基材表面撞合模型,将熔覆层分为:基体侧扩散区、撞合互混区、熔覆层侧扩散区,指出基体侧扩散区的大小、熔池结晶时原子扩散能力和程度决定熔覆层与基体界面及附近的组织结构。并在此基础上采用显微组织分析和扫描电子显微组织、成分分析、透射电子显微分析、力学性能分析等方法,研究了工艺参数对熔覆层的组织、性能及熔覆层与基体结合界     

渗铜量对颗粒强化铁基材料显微组织的影响

采用烧结-熔渗和后续热处理工艺制备了Co-Cr-Mo-Si颗粒强化的铁基粉末冶金材料,利用光学显微镜、扫描电镜和能谱分析技术,研究了不同渗铜量对材料显微组织的影响.研究表明:Co-Cr-Mo-Si硬颗粒单独存在于基体中,起颗粒强化的作用;未渗铜时,孔洞多,硬颗粒与基体界面清晰可见,结合强度差,随着渗铜量的增多,合金元素扩散程度提高,硬颗粒与基体界面结合强度好;材料的孔隙度减小,碳化物弥散分布程度提高;采用熔渗工艺并合理控制渗铜量,可获得组织均匀化、各相界面结合较好的铁基粉末冶金材料.     

金属粉末选择性激光烧结成形机制的研究

分析了纯金属粉末、预合金粉末和多组分金属粉末的选择性激光烧结成形机制;详细讨论了粉末的化学成分和物理性质,激光功率、扫描速率、扫描矢径、扫描间距等激光参数以及粉层厚度、粉床预热温度、保护气氛等工艺参数对成形机制的影响;并简要讨论了金属粉末选择性激光烧结技术的进一步研究方向.     

Effects of processing parameters on direct laser sintering of multicomponent Cu based metal powder

Abstract

Direct laser sintering of a multicomponent Cu based metal powder was successfully processed through the mechanism of liquid phase sintering with partial melting of the powder. The effects of processing parameters such as laser power, scan speed, scan line spacing and layer thickness on the densification and microstructural evolution of the laser sintered powder were investigated. It was found that with increasing laser power or decreasing scan speed, the density of the sintered parts increased and the microstructures became denser. However, the combination of higher laser powers (>400 W) and higher scan speeds (≥0·06 ms^?1) gave rise to 'balling' effect. A successive transition from discontinuous scan tracks to coherently joined ones occurs with decreasing scan line spacing. Lowering the thickness of the powder layer promises an improvement in bonding coherence between sintered layers. A single factor termed 'energy density by volume' is defined to evaluate the combined effect of various processing parameters on the density of laser sintered powder. With increasing the energy density by volume up to ～0·16 kJ mm^?3, the densification rate is relatively high. However, with intensifying the energy density over ～0·23 kJ mm^?3, the mechanism of particle bonding may change into full melting/solidification, leading to a decrease in the sintered density.     

WC–Co particulate reinforcing Cu matrix composites produced by direct laser sintering

Experimental investigations on the development of the WC–10%Co particulate reinforcing Cu matrix composite material have been conducted using direct laser sintering. The chemical compositions and microstructures of the laser processed material have been characterized using X-ray diffraction (XRD), energy disperse X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), and atomic force microscope (AFM). An excellent interfacial bonding between the reinforcement and the matrix was obtained. The WC reinforcing particulates typically had two distinct morphologies, i.e., partially dissolved and smoothed or completely dissolved and refined. The effects of the WC–Co content on the microstructural characteristics and resultant properties of the laser sintered parts have been studied. It was found that lowering the amount of WC–Co resulted in the insufficient reinforcement, while at a higher amount of WC–Co the significant agglomeration of the WC reinforcing particulates occurred. A homogeneous sintered structure with a high average hardness of HV_0.1384.6 was obtainable using 30 wt.% WC–Co.     

Densification and microstructural evaluation during laser sintering of M2 high speed steel powder

Abstract

In the present work, the densification and microstructure of M2 high speed steel powder processed by direct laser sintering method was studied. Test specimens were produced using a 200 W continuous wave CO₂ laser beam at different scan rates ranging from 50 to 175 mm s^?1. The building process was performed under argon and nitrogen atmospheres in order to evaluate the role of sintering atmosphere. It was found that the sintered density strongly depends on the laser scan rate and thus on the duration time of the laser beam on the surface of the powder particles. Generally, with a decrease in the scan rate higher densification was obtained. However, formation of large cracks and delamination of the sintered layers is feasible at low scan rates. The results also demonstrated that sintering under argon atmosphere yields better densification compared to a nitrogen atmosphere, in particular at higher scan rates. The microstructure of laser sintered parts consisted of large and elongated pores parallel to the building direction. The metal matrix structure was found to be heterogeneous, i.e. carbon rich austenite was formed due to carbon segregation. This structure consisted of fine cellulars or dendrites of martensite and retained austenite. This article describes the influence of manufacturing parameters on the densification of laser sintered M2 high speed steel powder. The microstructural features of the processed parts are also addressed.     

2D C/C复合材料微观结构与力学性能的研究

采用等温化学气相渗透方法,通过调整沉积工艺,制备了具有不同微观组织结构的2D C/C复合材料.利用偏光显微镜(PLM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)结合选区电子衍射(SAED),研究了热解炭基体微观组织结构,借助万能试验机测试了材料的三点弯曲性能.结果表明:层状高织构(HT)热解炭基体占优时C/C复合材料表现为假塑性断裂;扁平片状中织构(MT)热解炭与颗粒状各向同性层热解炭(ISO)有利于提高材料的弯曲强度;HT基体与炭纤维界面结合良好,界面处不存在非HT织构,但取向角(OA)略有增大.     

10Ni5CrMoV钢奥氏体焊缝接头熔合区马氏体带的显微组织

本文研究了A507填充10Ni5CrMoV钢接头熔合区马氏体带的显微组织。"原位取样"TEM分析表明熔合区存在板条马氏体、孪晶马氏体、奥氏体、贝氏体和部分分解的板条马氏体混合组织;彩色金相显示熔合区存在马氏体和奥氏体混合组织;结合Schaeffler图分析结果,可以确定这种混合组织位于OM下熔合区后续熔化滞留层的马氏体带。     

Laser remelting of plasma sprayed NiCrAlY and NiCrAlY-Al2O3 coatings

Two types of plasma sprayed coatings (NiCrAlY and NiCrAlY-Al2O3) were remelted by a 5 kW cw CO2 laser. With increasing laser power and decreasing traverse speed in the ranges of 200 similar to 700 W and 5 similar to 30 mm/s respectively, the melted track grew in width and depth. In the optimum range of laser parameters, a homogeneous remelted layer without voids, cavities, unmelted particles and microcracks was formed. On the surface of remelted layers, Al2O3 and YAlO3 were detected. As a result of isothermal oxidation tests, weight gains of laser remelted coatings were obviously lower than that only plasma sprayed, especially laser remelted NiCrAlY-Al2O3 coatings. The effects of laser remelting and incorporation of Al2O3 second phase in NiCrAlY matrix on high temperature oxidation resistance were discussed.     

Selective laser sintering of gas atomized M2 high speed steel powder

Selective laser sintering of the gas atomized M2 high speed steel powder was performed using laser powers of 2.5–100 W, scan rates of 1–30 mm/s and scan line spacings of 0.15–0.75 mm. With increasing laser power, the sintered surface varied from open/closed pores to a fully dense structure. Large lateral pores were found in the sintered surface of samples using high scan rates. For fully dense samples, smooth surfaces could be achieved using large scan line spacing. The as-supplied and sieved M2 powder particles with size ranging from 0.04 to 400 m and 53 to 150 m, respectively, were found to give better laser sinterability as compared with those powder particles with finer (<38 m) or coarser (>150 m) sizes.     

Laser Remelting of Plasma Sprayed NiCrA1Y and NiCrAlY-A12O3 Coatings

Two types of plasma sprayed coatings (NiCrAIY and NiCrAIY-AI2O3) were remelted by a 5 kW cw CO2 laser. With increasing laser power and decreasing traverse speed in the ranges of 200～700 W and 5～30 mm/s respectively, the melted track grew in width and depth. In the optimum range of laser parameters, a homogeneous remelted layer without voids, cavities, unmelted particles and microcracks was formed. On the surface of remelted layers, AI2O3 and YAIO3 were detected.As a result of isothermal oxidation tests, weight gains of laser remelted coatings were obviously lower than that only plasma sprayed, especially laser remelted NiCrAIY-AI2O3 coatings. The effects of laser remelting and incorporation of Al2O3 second phase in NiCrAIY matrix on high temperature oxidation resistance were discussed.     

Surface laser treatment of ductile irons

The effect of the laser surface treatment of three types of ductile iron (Grades 60-40-18, 80-55-06 and 100-70-03) was studied. Using a continuous CO₂ laser with a square 10 mm × 10 mm beam and uniform power density, the effect of beam scan rate at 2.5 and 5 kW power output was investigated. At each power rate, a range of scan rates was used to produce treatments with and without surface melting. The microstructure and hardness of the different zones of the treated material were analysed. It was found that layers of white iron of the same depth were produced in the three test irons when the operating conditions melted the surface material. Surface porosity can be eliminated by melting, although transverse cracks appeared on the surface with this treatment. Surface martensitic hardening produced a layer of uniform hardness only in the case of the grade 100-70-03 ductile iron with a perlitic matrix.     

45#钢高速冲击穿孔的显微组织

借助烧结的W合金圆柱体垂直冲击60mm厚的45^#热轧钢板实验,利用扫描电镜和光学金相显微镜研究了45^#钢高速冲击穿孔的显微组织。冲击波使穿孔周围的晶粒破碎,冲击引起的材料变形功转变为热能,以及侵彻过程中的摩擦作用,使穿孔表面熔化,靠近熔化区的晶粒发生再结晶。从穿孔表面到钢板内部可分为：熔化快凝层、再结晶细晶层、变形细晶层、形变层和正常基体组织。在细晶层和形变层中,铁素体晶粒的变形量要远远大于珠光体,部分珠光体开裂,其周围形成微裂纹和微孔洞。钢中的硫化锰夹杂在变形中被剧烈拉长。由于铁素体的塑性,钢板的破坏方式为延性扩孔。