Laser processing effects on Ti−45Nb alloy surface,corrosive and biocompatible properties

The Ti−45Nb(wt.%)alloy properties were investigated in relation to its potential biomedical use.Laser surface modification was utilized to improve its performance in biological systems.As a result of the laser treatment,(Ti,Nb)O scale was formed and various morphological features appeared on the alloy surface.The electrochemical behavior of Ti−45Nb alloy in simulated body conditions was evaluated and showed that the alloy was highly resistant to corrosion deterioration regardless of additional laser surface modification treatment.Nevertheless,the improved corrosion resistance after laser treatment was evident(the corrosion current density of the alloy before laser irradiation was 2.84×10^(−8)A/cm^(2),while that after laser treatment with 5 mJ was 0.65×10^(−8)A/cm^(2))and ascribed to the rapid formation of a complex and passivating bi-modal surface oxide layer.Alloy cytotoxicity and effects of the Ti−45Nb alloy laser surface modification on the MRC-5 cell viability,morphology,and proliferation were also investigated.The Ti−45Nb alloy showed no cytotoxic effect.Moreover,cells showed improved viability and adherence to the alloy surface after the laser irradiation treatment.The highest average cell viability of 115.37%was attained for the alloy laser-irradiated with 15 mJ.Results showed that the laser surface modification can be successfully utilized to significantly improve alloy performance in a biological environment.

Surface nanostructure formation mechanism of 45 steel induced by supersonic fine particles pombarding

By means of supersonic fine particles bombarding （SFPB）,a nanostructured surface layer up to 15 μm was fabricated on a 45 steel plate with ferrite and pearlite phases. To reveal the grain refinement mechanism of SFPB-treated 45 steel,microstructure features of various sections in the treated surface were systematically characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Grain size increases with an increase of depth from the treated surface. Plastic deformation and grain refinement processes are accompanied by an increase in strain. Plastic deformation in the proeutectoid ferrite phases has precedence over the pearlite phases. Grain refinement in the ferrite phases involves： the onset of dislocation lines （Dls）,dislocation tangles （DTs） and dense dislocation walls （DDWs） in the original grains; the formation of fine lamellar and roughly equiaxed cells separated by DDWs; by dislocation annihilation and rearrangement,the transformation of DDWS into subboundaries and boundaries and the formation of submicron grains or subgrains; the successive subdivision of grains to finer and finer scale,resulting in the formation of highly misoriented nano-grains. By contrast,eutectoid cementite phase accommodated strain in a sequence as follows： onset of elongated,bended and shear deformation under deformation stress of ferrites,short and thin cementites with a width of about 20-50 nm and discontinuous length were formed. Shorter and thinner cementites were developed into ultra-fine pieces under the action of high density dislocation and strains. At the top surface,some cementites were decomposed under severe plastic deformation. Experimental evidences and analysis indicate that surface nanocrystallization of 45 steel results from dislocation activities,high strains and high strain rate are necessary for the formation of nanocrystallites.

Microstructure and corrosion resistance of Fe-Al intermetallic coating on 45 steel synthesized by double glow plasma surface alloying technology

A binary Fe-Al alloyed layer was synthesized on 45 steel by means of double glow plasma surface alloying technique. The corrosion-resisting layer prepared is composed of a sedimentary layer and a diffusion layer, with a total thickness of about 180 μm. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. The ideal profile is beneficial to the metallurgical bonding of the surface alloying layer with substrate materials. The microstructure of both layers consists of the Fe-Al intermetallic compound, which is FeAl with B2 structure in the sedimentary layer and Fe3Al with incompletely ordered DO3 structure in the diffusion layer. The protective film exhibits high micro-hardness. In comparison with the substrate of 45 steel, the corrosion resistance of the aluminized sample is much higher in 2.0% Na2S and 0.05 mol/L Na2SO4 + 0.5 mol/L NaCl mixed solutions.

Impact of Microstructural and Surface Modifications on the Ti-45Nb Alloy’s Response to Bio-Environment

The Ti-45Nb (mass%) alloy’s corrosive and biocompatible response in simulated physiological conditions was investigated before and after its additional high-pressure torsion (HPT) and laser irradiation processing. The grain size reduction from 2.76 µm to ~ 200 nm and the appearance of laser-induced morphologically altered and highly oxidized surface led to the significant improvement of alloy corrosion resistance and cell–implant interaction. Moreover, an additional increase of the laser pulse energy from 5 to 15 mJ during the alloy irradiation in the air led to an increase in the surface oxygen content from 13.64 to 23.89% accompanied by an increase of excellent cell viability from 127.18 to 134.42%. As a result of the controlled alloy microstructural and surface modifications, the formation of protective bi-modal mixed Ti- and Nb-oxide external scale was enabled. The presence of this surface oxide scale enhanced the alloy’s resistance to corrosion deterioration and simultaneously boosted cell viability and proliferation.

紫外纳秒激光扫描处理冷拔45钢的表面性能研究

采用波长355 nm的紫外纳秒脉冲激光对45钢冷拔平键表面扫描处理,制备了不同工艺参数下的试样,研究了表面硬度、表面粗糙度等的变化规律。结果表明:激光扫描可使45钢冷拔平键的表面硬度由301.7 HV0.2提高到442.8 HV0.2,提高幅度近50%。激光扫描硬化层的厚度约30μm。振动抛光处理可降低激光扫描表面的粗糙度而保持其较高的显微硬度。

Surface performance of workpieces processed by electrical discharge machining in gas

The surface performance of workpieces processed by electrical discharge machining in gas(dry EDM)was studied in this paper.Firstly,the composition,micro hardness and recast layer of electrical discharge machined(EDMed)surface of 45 carbon steels in air were investigated through different test analysis methods.The results show that the workpiece surface EDMed in air contains a certain quantity of oxide,and oxidation occurs on the workpiece surface.Compared with the surface of workpieces processed in kerosene,fewer cracks exist on the dry EDMed workpiece surface,and the surface recast layer is thinner than that obtained by conventional EDM.The micro hardness of workpieces machined by dry EDM method is lower than that machined in kerosene,and higher than that of the matrix.In addition,experiments were conducted on the surface wear resistance of workpieces processed in air and kerosene using copper electrode and titanium alloy electrode.The results indicate that the surface wear resistance of workpieces processed in air can be improved,and it is related with tool material and dielectric.

模拟海水环境下动态腐蚀后45钢拉伸损伤演化行为

为研究模拟海水环境下腐蚀后45钢的拉伸损伤,采用腐蚀反应釜、声发射检测仪(AE)、扫描电镜(SEM)对腐蚀试样进行拉伸力学性能试验,获取载荷下拉伸过程的AE信号参数、腐蚀试样表面与断口形貌。结果表明:试样拉伸过程中产生的AE信号相对能量主要集中于弹性阶段、屈服阶段和强化阶段;AE信号数量从大到小按强化阶段>弹性阶段>屈服阶段排列。随载荷增加,在弹性阶段试样开始出现损伤,屈服阶段损伤略有降低,强化阶段前期损伤大幅度增加,其中弹性阶段拉伸损伤大于屈服阶段。腐蚀时间影响试样的腐蚀程度,28 d腐蚀试样的腐蚀程度明显大于14 d腐蚀试样,28 d腐蚀试样表面附着大量颗粒状腐蚀物,然而14 d腐蚀试样在加载拉伸下的每一阶段的损伤大于28d的腐蚀试样。

表面感应淬火对45钢滚动磨损特性的影响

针对传统热处理后45钢耐磨性较低的缺点,研究了正火+表面感应淬火热处理后45钢相对ZG31Mn2Si摩擦副的滚动磨损特性和磨损机理。测试了试验载荷、材料硬度与磨损失重的关系,采用扫描电镜分析了感应淬火热处理后不同硬度45钢的磨损形貌及变化规律。结果表明:当载荷恒定,磨料硬度Ha大于被磨材料45钢硬度Hm时,45钢随着感应淬火后自身硬度的提高,耐磨性明显提高,为硬磨料磨损;Ha<Hm时,随着材料硬度的提高,磨损量变化很小,为软磨料磨损;其滚动磨损机理随着表面感应淬火后硬度的升高由塑变磨损转变为犁沟磨损。

超音速微粒轰击45钢表面纳米化的研究

采用超音速微粒轰击技术（SFPB）对由铁素体和珠光体组成的45钢进行表面纳米化处理,在材料表面制备了纳米结构表层,利用X射线衍射、扫描电镜、透射电镜等分析技术研究了表面纳米结构层不同深度的微观组织结构特征.研究表明：经SFPB处理后,材料表层发生了严重的塑性变形,形成了由铁素体和渗碳体组成的纳米结构层;随着处理时间的增加纳米结构层的厚度由几微米增加到15μm（晶粒尺寸〈100 nm）;在材料的最表层形成了晶粒尺寸约15 nm的具有随机取向的等轴晶,纳米晶粒尺寸随着距表面距离的增加增大;在距表面约为15μm处,存在平均晶粒尺寸约100 nm的等轴晶和具有相近尺寸的胞状结构;在约30μm处,大量的高密度位错墙分别将铁素体相和珠光体相分割成尺寸在200~500 nm的胞状结构.分析表明45钢表面纳米化主要是位错运动的结果.

45钢表面制备V形凹槽及其摩擦学特性

采用声光调Q固体Nd:YAG激光器在45钢试样表面制备了V形凹槽织构,利用UMT-2的销盘式摩擦方式考察了V形凹槽的几何参数对表面摩擦性能的影响。结果表明:45钢表面制备的V形凹槽织构,在油润滑条件下能有效减小表面的摩擦因数;特别是在载荷较低、速度较大的工况下,织构面的平均摩擦因数最大可比未织构面减小64%。在试验范围内,平均摩擦因数普遍随着V形凹槽角度的增加而减小,随着边长的增大而减小,存在最优的横向和横向槽间距使得平均摩擦因数达到最小。

利用强流脉冲电子束对45^#钢进行表面改性

利用强流脉冲电子束对45#钢进行了表面改性处理,并对其显微组织和改性机制进行了分析和讨论。结果表明:材料近表层的显微组织沿电子束注入方向大致可分为4层:熔化层(3～10μm)、热影响层(10～50μm)、应力影响层(50～250μm)、基体组织(大于250μm);显微硬度随轰击次数的增加而增加,最大值出现在50μm左右;多次轰击可以提高耐磨性。

45~#钢表面纳米晶层的高温磨损特性

通过增压喷丸方式使45#钢实现表面纳米化,采用MMU-5G高温材料端面磨损试验机进行45#钢纳米晶层摩擦磨损性能随温度变化的试验,利用TEM表征喷丸后表层的组织,DSC与显微硬度研究纳米层的热稳定性,XPS和SEM表征磨损表面的成分及形貌.结果发现:当温度低于200℃时,喷丸样品表面硬度高,有效减少实际接触面积,耐磨性能优于未喷丸样品;在200～400℃之间时,纳米化样品表层组织结构中存在大量的晶界、位错、空位等缺陷为氧原子与金属原子提供更多的扩散通道,加速疏松的Fe2O3氧化物的形成与脱落,耐磨性能低于未喷丸样品;在400～550℃之间时,喷丸样品由于回复与再结晶,与未喷丸的耐磨性能基本一致.

45钢激光相变硬化和感应加热表面淬火硬化后的组织和性能

采用光学显微镜、电化学工作站和力学性能测试等对45钢在激光相变硬化和感应加热表面淬火两种不同淬火方法下的淬硬层组织、导电性能、耐腐蚀性能进行了对比分析。结果表明：经过激光相变硬化处理过的45钢试样导热性要低于感应加热表面淬火试样,而经过表面淬火处理的试样导热性明显低于未经过处理的试样;在相同扫描速度4 mm/s下,感应加热表面淬火试样的淬硬层深度远大于激光相变硬化试样的淬硬层深度,淬硬层组织分布相对弥散,马氏体转化率较低,激光相变硬化试样淬硬层组织晶粒相对细小,淬硬层较薄,转化马氏体组织较为均匀;同时激光相变硬化试样的腐蚀程度小于感应加热表面淬火试样,而感应加热表面淬火试样腐蚀后的硬度值及强度不如前者,总体而言,激光相变硬化试样的淬火效果要优于感应加热表面淬火试样的淬火效果。

扫描速率对45钢表面激光熔覆结构和性能的影响

在45钢表面激光熔覆Ni基复合涂层。利用金相显微镜、XRD衍射仪和显微硬度计研究了扫描速率对表面结构和显微硬度的影响。结果表明:不同工艺熔覆后试样均由表面熔覆区、结合区和基体三部分组成,并达到冶金结合。复合涂层主要由FeNi3和Ni3B相组成。熔覆层显微硬度平均值都超过基体,最大硬度比基体高33%。相同激光功率条件下,扫描速度越慢,性能越好。

45钢激光表面合金化

为提高45钢的表面硬度,达到表面改性的目的,对表面镀镍的45钢进行了激光表面合金化,对合金化的表面进行了定性和定量分析。结果表明:合金化层组织为细小的枝晶,明显优于基体组织;合金化层平均硬度比基材提高3倍。

45钢表面状态对聚晶金刚石复合片钎焊性能的影响

制备了不同表面状态的45钢试样,采用BAg612银焊钎料焊接45钢试样与聚晶金刚石复合片（Polycrystalline diamond compacts,PDC）,研究了45钢表面状态对PDC钎焊性能的影响。结果表明：45钢表面状态为100目喷砂面和磨削面时,钎料润湿性较好,钎焊试样的剪切强度较佳,约为230 MPa。当45钢表面为喷砂态时,随着喷砂粒径的减小,钎料的润湿性和剪切强度呈增大趋势。45钢磨削态的钎焊件的剪切强度高于抛光态的剪切强度,这可能是钎料在磨削态表面的润湿性较在抛光态表面的好,且磨削沟槽使得钎焊面积增加的缘故。

45钢表面增压喷丸纳米化及其耐磨性研究

采用增压喷丸方式对45钢进行表面处理,在材料表面制得纳米结构表层,利用SEM、TEM、XRD等方法对纳米结构表层进行了观察与分析,采用盘-销式摩擦磨损试验机研究了纳米化前后表面的磨损性能。结果表明:增压喷丸使45刚表面发生严重的塑性变形,变形厚度约30μm,表层纳米晶尺寸约65 nm,硬度比基体提高2倍;在低载油润滑条件下45钢表面纳米化后表现出优异的耐磨性能。

45钢干摩擦三维表面形貌特征研究

利用HST-100销-盘式摩擦磨损试验机考察干摩擦条件下45钢销试样的摩擦学性能,采用nanofocus三维表面轮廓测定仪检测其磨损表面形貌。研究表明,摩擦系数和表面高度偏差随滑动速度和载荷的变化存在一定的相关性,但二者随速度变化的相关性更强;陡峭度与复杂条件下摩擦系数呈线性变化,摩擦系数越大,陡峭度越大,尖峰宽度越小。

45钢激光WC合金化组织与性能的研究

在45钢表面进行了碳化钨(WC)激光合金化实验,利用金相显微镜、维氏硬度计等设备检测了合金化层的组织和性能。实验表明:激光合金化层组织致密,晶粒细化,与基体呈冶金结合。其中,合金化区为含碳量过饱和的奥氏体树枝晶组织,热影响区为板条状淬火马氏体组织。合金化区平均硬度700 HV0.2,相变硬化区平均硬度550 HV0.2,硬度呈梯度过渡。通过与氮化试样的比较,表明激光合金化试样的强化层深度、平均硬度均高于氮化试样。45钢零件经激光合金强化后,使用寿命大大提高。

超声表面滚压处理对45钢摩擦学性能的影响及机理

采用超声表面滚压处理(USRP)技术对45钢表面进行强化处理,通过表面形貌和表层显微组织观察、表面粗糙度和摩擦磨损性能测试,研究了USRP对该钢摩擦学性能的影响及机理。结果表明:USRP试样的表面粗糙度由未处理试样的3.2μm降低到0.23μm;显微组织得到了细化,晶粒取向趋于随机分布,有大角度晶界出现;表面显微硬度比未处理试样的提高约56%,强化层厚度达到400μm;USRP试样的摩擦因数小于未处理试样的,磨损量为未处理试样的1/4;未处理试样磨损过程中表面材料呈"片块状"脱落,磨损机制为黏着磨损,USRP试样磨损表面上存在犁皱形成的沟槽,磨损机制为磨粒磨损。