NiTi合金激光熔凝处理及其生物腐蚀性能研究

目的 通过对NiTi合金表面进行激光熔凝处理,从而提高NiTi合金的耐腐蚀性能。方法 利用紫外激光器对NiTi合金进行表面熔凝处理,借助扫描电子显微镜(SEM)、光学显微镜(OM)、能量色散X射线光谱仪(EDX)和X射线衍射仪(XRD)等技术手段,研究了激光熔凝处理前后NiTi合金的表面显微组织、成分和相结构。测试了激光熔凝处理前后NiTi合金表面与模拟体液(SBF)的接触角、熔凝层的显微硬度等表面性能。通过全浸腐蚀试验和电化学测试,研究了熔凝层在SBF溶液中的生物腐蚀性能,并分析了腐蚀机理。结果 NiTi合金经过激光熔凝处理后,在合金的表层形成了厚度为90~150 μm的熔凝层,熔凝层主要由TiO2、β相以及少量的TiO相组成。合金表面的平均显微硬度提高了153~279HV,合金的表面接触角增大,由亲水性转为疏水性。相较于未处理的样品,熔凝处理后的样品在SBF溶液中的腐蚀电位分别正移了435 mV和413 mV,腐蚀电流密度分别下降了83%、62%左右。熔凝处理后的样品在SBF溶液浸泡168 h后,SBF溶液中的Ni²⁺浓度下降了约1/3。结论 以适当的激光加工参数对NiTi合金进行激光熔凝处理,可在NiTi合金表面形成致密的氧化膜,这层氧化膜和熔凝层可以有效地抑制NiTi合金在SBF溶液中的点腐蚀行为。     

激光表面快速熔凝Fe—Sb合金的显微组织和硬度

研究了激光表面快速熔凝Fe－Sb合金的显微组织和硬度，并基于热流模型计算了治区的几何尺寸和冷速。     

合金激光表面熔凝组织的超塑扩散连接机理

研究了合金激光表面熔凝组织在超塑扩散连接中的细晶超塑变形和扩散机。对金属高温力学行为和晶界滑移微观机制的分析表明，激光表面改性获得的细晶组织，在连接过程中发生超塑变形，加速了空隙闭合；激光表面熔凝组织超塑扩散连接中出现了以晶界扩散为主的扩散模式，晶粒细化带来的晶界体积百分数的增加，提高了扩散速率；非平衡组织扩散性能以及非平衡晶界迁移加速了界面区空位、位错消除和再结晶过程。     

激光表面熔凝处理过共晶Al-Si合金的疲劳裂纹扩展行为

试验研究了Al-20%Si合金在激光表面熔凝处理后的显微组织特征及激光表面熔凝处理对合金疲劳裂纹扩展形为的影响。结果表明,激光表面熔凝处理使试验合金的显微组织得到了明显细化,熔凝层主要由细小的初生Si、-αAl及Al-Si共晶相组成,熔凝层的硬度显著提高;在应力比R为0.1和0.5的试验条件下,激光表面熔凝处理显著提高了试验合金的疲劳裂纹扩展抗力。     

不锈钢激光表面熔凝处理的组织特征

不锈钢经激光表面熔凝处理后，其组织形态发生了显著的变化，在表面熔凝层中分别出现白亮带、细胞晶、胞枝结构以及紊乱枝晶组织，对其形成原因进行了分析．在激光熔池中观察到典型的胞枝转变，对转变的临界条件进行了深入研究，结果表明：实验确定的胞枝转变临界速度与最近提出的ＢＪＴ模型的预言值符合得较好．     

球墨铸铁凸轮轴的激光表面熔凝处理

分析了激光表面熔凝处理后球墨铸铁凸轮轴硬化层的组织和性能特点，并与其它强化方法进行了比较。结果表明，采用适当的激光表面熔凝处理工艺参数，可以在表面获得搭接均匀、表面硬度大于80HRA和厚度达1．0mm的硬化层；硬化层由熔凝层和淬硬层组成，其中熔凝层的基体组织主要为细小、均匀并且有一定方向性的亚共晶莱氏体，淬硬层主要由石墨球及其周围的硬质环、细马氏体和铁素体基体所组成。与其它铸铁凸轮轴强化方法相比，激光表面熔凝处理具有表面硬度高、组织细小均匀、零件畸变小和不影响心部性能等优点。     

LD冷作模具钢激光表面熔凝研究

研究了冷作模具LD钢经不同工艺参数激光熔凝处理后的显微组织及性能。结果表明,激光功率P=3500 W,扫描速度v=20 mm/s,光斑直径d=5 mm时,处理效果较为理想。由表及里依次为熔凝层、淬火层、热影响层和基体。熔凝层又依次分为表层等轴晶区,柱状晶区和等轴晶+胞状晶区。等轴晶区和柱状晶区原有的带状、块状碳化物全部溶解,胞状晶区原有的碳化物基本保持原状,新晶粒明显细化并均匀分布。硬化层总深度可达1.0 mm;平均硬度可提高15%左右,耐磨性和耐腐蚀性显著提高。如果能量密度过大,在熔凝层容易产生微裂纹甚至宏观裂纹,破坏材料性能。     

镁合金激光表面熔凝处理研究进展

镁合金是优异的轻量化材料和极具潜力的人体植入材料,但其耐蚀性差。激光表面熔凝技术可快速在镁合金表面形成晶粒细小的熔凝层,改善镁合金表面微观形貌和组织结构,对提高其表面耐蚀性和生物相容性有重要作用。综述了近年来镁合金激光表面熔凝处理的相关研究工作,分析了熔凝处理工艺对镁合金微观结构、成分、润湿性、耐蚀性和生物相容性的影响。总结并展望了激光熔凝处理在镁合金的组织结构转变、腐蚀机理及力学行为、降解行为和生物相容性等方面的发展方向。     

ZL101合金激光熔凝强化处理

采用5 kW CO2激光器对ZL101合金表面进行激光熔凝强化,用光学显微镜、扫描电镜和显微硬度计对熔凝层与铝合金基体的界面结合区的组织结构和显微硬度进行分析。结果表明,重熔后的ZL101显微组织分为熔凝区、热影响区和基体。熔凝区与基体相比,组织明显细化,共晶Si由针条状变为细小颗粒状。表面熔凝区的硬度较基体提高了20%。     

Ti-24Al-17Nb-0.5Mo合金激光熔凝处理后的组织特征

采用不同工艺对Ti3Al-Nb合金进行了激光熔凝实验.分别运用OM,SEM,XRD和EP对熔化区显微组织进行了观察与分析.结果表明,熔化区由成分偏离平衡成分的β相组成,呈弧形分层特征,有贯穿层间的晶界;晶粒中有特征尺寸为400-750 nm的柱状亚结构和等轴亚结构.基于三维热传导模型,借助Mathematic 4.0计算软件对熔池形状和温度分布进行了数值模拟,计算结果与实验吻合.     

Mg67Zn28Ca5合金激光表面非晶化处理及其生物腐蚀性能研究

Mg-Zn-Ca合金因其较好的力学性能、良好的生物相容性和优异的可降解性,有望在人体骨组织植入材料得到推广应用,但由于镁合金耐生物腐蚀性能较差,限制了其临床的进一步应用。通过激光表面非晶化处理对共晶成分的Mg67Zn28Ca5合金进行了表面改性,研究了激光扫描速度对Mg67Zn28Ca5 合金表面非晶复合涂层的显微组织和相组成的影响;测试了合金表面改性前后在人工模拟体液中的生物腐蚀行为。研究结果表明,经激光表面非晶化处理后样品表面主要由大量的非晶和极少量的晶态物质组成。随着激光扫描速度的增大,合金表面形成的非晶相越多。晶相的形成主要是受到后续激光加工的热影响而产生热激活,部分非晶相发生了形核长大。与铸态镁合金相比,非晶复合涂层在人工模拟体液中的腐蚀电位正向偏移了0.16 V,腐蚀电流密度下降了约13倍。合金表面少量晶相的存在,使之成为表面腐蚀的活性通道,对合金表面的腐蚀性能产生轻微的影响。通过激光表面改性处理,可有效改善Mg67Zn28Ca5合金的耐生物腐蚀性能,在生物医用植入方面展现出良好的应用前景。     

Effect of nano-CeO2 on cobalt-based alloy laser coatings

Cobalt-based alloy coatings with/without nano-CeO₂ addition prepared by a 5 kW CO₂ laser on Q235 low carbon steel were introduced. The effects of nanoparticles on the macro-quality, microstructure, phase composition, and wear resistance of the coatings were investigated. The microstructure and phases composition of the coatings were analyzed using Olympus-Pme-3 type microscope, Philip Xl 30 type scanning electron microscope and XD-3A type X-ray diffractometer (XRD). The wear resistance was tested using MM-200 type sliding wear machine, and the wear mechanism was analyzed by JSM-35C type scanning electron microscope (SEM). The results showed that defect (such as crack, gas hole, etc.) -free coatings were obtained. There existed γ-Co and Cr₂₃C₆ in cobalt-based alloy coatings. Another two phases of CeCo₂ and -Co were identified with nanoparticles addition. Fine microstructure and equiaxed dendrite were obtained by adding nano-CeO₂. The relative wear resistance is improved with the increased amount of nano-CeO₂, and the coatings with the best wear resistance when laser power was 2.0 kW by adding 1.5 wt.% CeO₂. The mechanism was found from abrasive/adhesive wear to fretting wear. The wear resistance decreased with 2.0 wt.% CeO₂ addition.     

Effect of laser surface melting on friction and wear behavior of AM50 magnesium alloy

In the present study, an attempt has been made to enhance tribological properties of AM50 magnesium alloy by laser surface melting (LSM) with a 2 kW continuous wave CO₂ laser. The microstructure of the laser surface melted zone consists of fine columnar dendrites growing epitaxially from the liquid-solid interface. Microhardness of the melted zone was improved to 55-75 HV as compared to 40 HV of the substrate. The friction and wear behavior of the laser surface melted layer were investigated using a ball-on-flat apparatus under dry sliding condition. It was found that the friction coefficient curve of the laser surface melted layer was similar to that of substrate. They showed a lower initial friction coefficient about 0.18 that after the running-in period increased up to about 0.38. Furthermore, compared with the AM50 substrate, the wear volume of the laser surface melted layer was decreased by 42%, the wear resistance of the laser surface melted layer was improved.     

Li对快速凝固Mg96.5Gd2.5Zn1合金微观组织和力学性能的影响

本文考察了快速凝固条件下不同含量Li元素添加对长周期有序结构相增强Mg-Gd-Zn合金微观组织和力学性能的影响。结果表明,随着Li元素的添加,铸态合金中Gd、Zn溶质原子在镁基体晶粒中的过饱和度降低、(Mg,Zn)₃Gd晶界析出相增加、镁基体晶粒尺寸减小。而固溶处理后,随着Li含量的增加,合金中14H型长周期堆垛有序结构相(LPSO)的形成受到抑制,同时纳米/亚微米(Mg,Zn)₃Gd颗粒相大量析出,当Li为7.6at. %时合金中无LPSO形成。经热挤压变形后,合金中块状14H相发生扭着分层开裂、层片状14H相发生不同程度溶解、(Mg,Zn)₃Gd相破碎细化、基体发生不同程度再结晶;不加Li的Mg_96.5Gd_2.5Zn₁表现出最佳的力学性能(UTS=325,δ=9.5%),而含Li合金则随Li含量的增加,力学性能逐步下降。合金在不同条件下的组织转变机理及力学行为变化被进行了分析。     

热处理和熔炼方式改变对AlCoCrFeNiTi0.2高熵合金的影响

采用电弧熔炼方法设计制备了AlCo CrFeNiTi_(0.2)合金,发现铸态时的合金形成了B2相和bcc相,且室温压缩性能良好,压缩塑性为32.6%,屈服强度为1530.4 MPa,抗压强度为4035.0 MPa,硬度接近6000 MPa。在550、800和1050℃对其进行热处理,采用水冷的方式以保存高温相,3个温度对应的相组成分别为bcc+B2、bcc+B2+fcc+σ和bcc+B2+fcc,热处理后合金脆性和硬度升高。采用磁悬浮熔炼制备了大块AlCo CrFeNiTi_(0.2)合金,该状态合金成分分布比较均匀,形成了bcc+B2+σ3相,在600℃时压缩塑性为35.0%,且仍能保持1486.7 MPa的屈服强度,耐高温性能较好。     

Microstructure and corrosion behavior of plasma electrolytic oxidation coated magnesium alloy pre-treated by laser surface melting

An AZ91D magnesium alloy was treated using duplex techniques of laser surface melting (LSM) and plasma electrolytic oxidation (PEO). The microstructure, composition and corrosion behavior of the laser melted surface, PEO coatings, LSM–PEO duplex coatings as well as the as-received specimen were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electrochemical corrosion tests, respectively. Especially, the effect of LSM pre-treatment on the microstructure, composition and corrosion resistance of the PEO coatings was investigated. Results showed that the corrosion resistance of AZ91D alloy was marginally improved by LSM due to the refinement of grains, redistribution of β-phase (Mg₁₇Al₁₂) and increase of Al on the surface. Both the PEO and duplex (LSM–PEO) coatings improved significantly the corrosion resistance of the AZ91D alloys, while the duplex (LSM–PEO) coating exhibited better corrosion resistance compared with the PEO coating.     

Laser surface cladding of MRI 153M magnesium alloy with (Al+Al2O3)

Laser surface cladding was carried out on a creep-resistant MRI 153M magnesium alloy with a mixture of Al and Al₂O₃ powders using a pulsed Nd:YAG laser at scan speeds of 21, 42, 63 and 84 mm/s. The Al₂O₃ particles partially or completely melted during laser irradiation and re-solidified with irregular shapes in the size range of 5-60 µm along with a few islands as large as 500 µm, within the grain-refined Mg-rich dendritic matrix. More than an order of magnitude improvement in wear resistance after cladding was attributed to the presence of ultra-hard Al₂O₃ particles, increased solid solubility of Al and other alloying elements, and a very fine dendritic microstructure as a result of rapid solidification in the cladded layer. However, corrosion resistance of the laser cladded alloy was reduced by almost an order of magnitude compared to that of the as-cast alloy mainly due to the presence of cracks and pores in the cladded layer.     

Study on laser surface melting of AZ31B magnesium alloy with different ultrasonic vibration amplitude

The laser surface melted layers were fabricated on AZ31B magnesium alloy by ultrasonic vibration-assisted using with different vibration amplitude. Microstructural evolution and corrosion resistance were studied systematically. The uniformity and compactness of the microstructure can be get further improved with the increase of vibration amplitude, while the coarse microstructure is observed at an even higher vibration amplitude. The melted layer with a reasonable vibration amplitude at the maximum outputs of 80% possess the highest microhardness, and the lowest corrosion current density as well as the minimal corrosion rate than the substrate. The results of electrochemical impedance spectra (EIS) and corrosion morphology are in agreement with potentiodynamic polarisation measurements, the charge transfer resistance (Rct) and corrosion area of the sample at 80% vibration amplitude are highest and smallest, respectively. Experimental results revealed that the melted layer fabricated at 80% of the maximum vibration amplitude output value exhibit the best anti-corrosion performance.     

激光表面熔凝处理对共晶铝硅合金疲劳裂纹扩展的影响

研究了共晶铝硅合金在激光表面熔凝处理后的显微组织变化及激光表面熔凝处理对合金疲劳裂纹扩展的影响.结果表明,激光表面熔凝处理使试验合金的表层微观组织发生显著变化,熔凝层中的初生α-Al枝晶相和共晶Si相均有明显细化,熔凝层的硬度显著提高;在应力比R为0.1和0.5的试验条件下,激光表面熔凝处理能显著提高共晶铝硅合金的疲劳裂纹扩展抗力.