LIBS对钛合金焊缝中成分的原位统计分布分析表征

钛合金凭借其强度高、耐蚀性好、耐热性高等特点已经被广泛应用于航天、海洋、生物医药等诸多领域,其中Ti-6Al-4V（TC4）合金的耐热性、强度、塑性、韧性、成形性、可焊性、耐蚀性和生物相容性均较好,已成为钛合金工业中的王牌合金。钛合金在激光焊接时,加入表面活性剂可以增加焊缝熔深、提高焊接效率、改善焊缝微观组织的不均匀性,但是可能会改变熔合区和焊缝区中元素含量及其分布状态,从而可能会对材料的性能产生一定的影响。运用LIBS分析技术对TC4钛合金焊接试样表面进行面扫描同步获得多元素成分信息,同时结合原位统计分布分析方法（OPA）,实现了对钛合金母材、熔合区、焊缝成分及其分布状态的快速表征,为活性剂的选择和焊接后钛合金的材料性能提供一种新的评价手段。选取了两个使用不同活性剂进行焊接的TC4钛合金薄板试样,选取焊缝纵切面方向作为分析面,采用320目的氧化铝砂纸进行表面处理,利用LIBSOPA系统进行成分分布统计表征。首先,对激发光斑和剥蚀条件进行条件优化,最终选择200 μm的激发光斑、10个预剥蚀脉冲10个剥蚀脉冲进行实验,并建立了钛合金中C,Al,V,Fe,Si和Ti六个元素的校准曲线（其中Si元素主要来自活性剂）;然后对钛合金焊接样品进行了区域扫描,并对元素含量和分布状态进行了统计表征。同时,在钛合金焊接样品的不同部位进行分区取样,采用高频红外法分析C元素含量,并与LIBSOPA结果进行比对,两种测试方法结果吻合。元素Al,V,Fe,Si和Ti分布结果与微束X荧光光谱法对应性较好。运用LIBSOPA 技术实现了对钛合金母材、熔合区、焊缝中多元素的成分分布表征,为快速判定钛合金焊缝中成分及分布状态提供了全新的评价表征手段。     

Influence of slight microstructural gradients on the surface properties of Ti6Al4V irradiated by UV

Ti6Al4V alloy is one of the most widely used materials for biomedical implants. Among its properties, it is remarkable the photoactivity displayed by its passive layer, which is mainly composed by titanium dioxide. However, variations in the processing conditions may yield to differences in the microstructure which can be reflected on the surface properties of the machined product. From contact angle measurements taken on different zones of samples removed from a commercial bar of Ti6Al4V, it has been shown that the modifications of the surface Gibbs energy suffered by the alloy under UV irradiation have a radial dependence. This behaviour is related to slight microstructural changes of the alloy, particularly with an increase in the volume fraction of the β-phase when moving to the interior of the sample, which alters the composition and/or microstructure of the passive layer along its radius. This study shows that gradients in the microstructure and physical properties are sample size dependent and are likely related to thermal gradients during processing.     

Microstructure and tribological behaviors of Ti6Al4V alloy treated by plasma Ni alloying

Ni modified layer was prepared on surface of the Ti6Al4V substrate by plasma surface alloying technique. Surface morphology, micro-structure, composition distribution, phase structure, and microhardness of the Ni modified layer were analyzed. Tribological performance of the Ni modified layer and Ti6Al4V substrate was investigated by using pin-on-disc tribometer. The results indicate that roughness of the Ni modified layer was increased due to formation of the micro-convex on the modified surface. The concentration of Ni gradually decreased from the surface to interior. The maximum content of Ni atoms was nearly 90%. The modified layer was composed of TiNi, Ti2Ni and Ti phases. The maximum microhardness of the Ni modified layer was about 677 HV_0.025 which was increased about two-fold of microhardness of the control Ti6Al4V substrate. Wear resistance of the Ni modified layer was improved obviously, and showed micro-abrasion wearing. The strengthened mechanism of the as-treated Ti6Al4V alloy is discussed.     

Crystallographic texture and microstructure evolution during hot compression of Ti–6Al–4V–0.1B alloy in the (α + β)-regime

Microstructure and texture are known to undergo drastic modifications due to trace hypoeutectic boron addition (~0.1 wt.%) for various titanium alloys e.g. Ti–6Al–4V. The deformation behaviour of such an alloy Ti–6Al–4V–0.1B is investigated in the (α?+?β) phase field and compared against that of the base alloy Ti–6Al–4V studied under selfsame conditions. The deformation microstructures for the two alloys display bending and kinking of α lamellae in near α and softening via globularization of α lamella in near β phase regimes, respectively. The transition temperature at which pure slip based deformation changes to softening is lower for the boron added alloy. The presence of TiB particles is largely held attributable for the early softening of Ti–6Al–4V–0.1B alloy. The compression texture of both the alloys carry signature of pure α phase defamation at lower temperature and α→β→α phase transformation near the β transus temperature. Texture is influenced by a complex interplay of the deformation and transformation processes in the intermediate temperature range. The contribution from phase transformation is prominent for Ti–6Al–4V–0.1B alloy at comparatively lower temperature.     

铝合金焊前激光清洗的等离子体光谱在线检测

铝合金焊接技术在工业生产、制造和维修等领域有广泛的应用,焊缝内存在气孔导致焊接质量降低是铝合金焊接技术的常见问题。由于铝合金表面金属氧化物是导致气孔生成的主要来源,对激光清洗过程进行在线检测,不但可以实时分析表面氧化物的清洗状态,而且可以避免基体表面因为过度清洗造成损伤或二次氧化。提出采用激光诱导等离子体光谱(LIBS)在线检测铝合金焊前激光清洗过程,表征清洗后铝合金基体的表面状态。LIBS技术可以对多元素成分同时检测,拥有较低的检出限和较高的准确性。搭建基于Andor Mechelle 5000光谱仪的铝合金焊前激光清洗在线检测系统,剔除空气环境对实验结果的影响,测试6061铝合金表面氧化物和铝合金基体的LIBS光谱,分析两者独特的元素特征谱线,采用X射线能谱(EDS)测试结果验证元素特征谱线的准确性,并探讨激光清洗过程LIBS技术在线检测的可行性。实验测试等离子体光谱谱线强度与激光能量密度之间的关系,获得单次脉冲激光去除铝合金表面氧化物的损伤阈值,结合X射线能谱的检测结果研究激光损伤阈值的成因及影响。研究激光清洗过程等离子体光谱特征谱线与脉冲次数之间的关系,提出基于O/Al特征谱线强度比值作为在线检测清洗效果及二次氧化损伤的评判依据。为验证该评判依据的准确性,将O/Al特征谱线强度比值随清洗次数的变化趋势与X射线能谱测试获得的氧元素原子百分比变化趋势进行对比。实验结果表明:采用200~700 nm范围内激光诱导等离子体谱线特征分析激光清洗状态,可以剔除空气环境的影响;氧元素和铝元素特征谱线准确反映出表面氧化膜与铝合金基体的成分差异;X射线能谱检测元素成分和含量表明氧元素含量随着激光清洗能量密度先减后增,单次清洗铝合金的二次氧化损伤的激光能量阈值为11.46 J·cm-2,小于损伤阈值的激光能量密度对铝合金基体的多次清洗未造成损伤,等离子体光谱特征谱线强度与表面清洗状态相关, 656.5 nm(OⅡ)/396.2 nm(AlⅠ)谱线强度比值≤1.5%为激光清洗干净的依据。研究结果有利于铝合金的激光清洗实时控制技术和焊接装置集成化。     

Single-pulse drilling study on Au,Al and Ti alloy by using a picosecond laser

Picosecond laser single pulse ablation of Au, Al and Ti alloy (Ti6Al4V) was experimentally investigated with a laser pulse width of 10 ps at a wavelength of 1064 nm for potential industrial micromachining applications. The diameters, depths and morphologies of the drilled craters were studied. Two novel phenomena were found: as hole diameters decreased with fluence, a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy, metallic materials with short electron-phonon coupling times (<10 ps), while Au showed no such transition: an isolated island structure was also observed on Au due to significant melt expulsion. A one-dimensional two-temperature model has been used to discriminate different ablation phenomena. It is shown that metallic materials with different electron–phonon coupling constant have different ablation characteristics in the ps regime. This study could be very helpful for metallic material micromachining with high repetition rate ps lasers pulses which indicates that high throughput may be achieved as well as good machining quality.     

Quantitative analysis of multi-element oxide thin films by angle-resolved XPS: Application to ultra-thin oxide films on MgAl substrates

An original procedure has been developed for the quantitative analysis and microstructural interpretation of angle-resolved X-ray photoelectron spectra (AR-XPS) of very thin (<6 nm), multi-element oxide films as grown on metallic binary alloy substrates by, e.g., thermal or plasma oxidation. To this end, first an approach has been given to retrieve the different metallic, oxidic and oxygen primary zero-loss (PZL) intensities from the measured AR-XPS spectra of the bare and oxidized alloy. The principal equations for the determination of the oxide-film thickness, composition and constitution from the resolved PZL intensities have been presented. On this basis, various corresponding calculation routes have been distinguished. The procedure has been applied to the case of very thin (<6 nm), mixed (Mg, Al)-oxide films on bare Mg-based MgAl substrates as grown by dry, thermal oxidation at room temperature. The results obtained on the thickness, composition, defect structure and constitution of the oxide-film have been discussed as function of the bulk Al alloying content and the applied partial pressure of oxygen.     

Interaction behaviors at the interface between liquid Al–Si and solid Ti–6Al–4V in ultrasonic-assisted brazing in air

Power ultrasonic vibration (20 kHz, 6 μm) was applied to assist the interaction between a liquid Al–Si alloy and solid Ti–6Al–4V substrate in air. The interaction behaviors, including breakage of the oxide film on the Ti–6Al–4V surface, chemical dissolution of solid Ti–6Al–4V, and interfacial chemical reactions, were investigated. Experimental results showed that numerous 2–20 μm diameter-sized pits formed on the Ti–6Al–4V surface. Propagation of ultrasonic waves in the liquid Al–Si alloy resulted in ultrasonic cavitation. When this cavitation occurred at or near the liquid/solid interface, many complex effects were generated at the small zones during the bubble implosion, including micro-jets, hot spots, and acoustic streaming. The breakage behavior of oxide films on the solid Ti–6Al–4V substrate, excessive chemical dissolution of solid Ti–6Al–4V into liquid Al–Si, abnormal interfacial chemical reactions at the interface, and phase transformation between the intermetallic compounds could be wholly ascribed to these ultrasonic effects. An effective bond between Al–Si and Ti–6Al–4V can be produced by ultrasonic-assisted brazing in air.     

Titanium plasma spectroscopy studies under double pulse laser excitation

Laser-induced breakdown spectroscopy (LIBS) was applied for parametric studies of titanium (Ti) plasma using single and double pulsed laser excitation scheme. Here a pulsed Nd:YAG laser was employed for generation of laser produced plasma from solid Ti target at ambient pressure. Several ionized titanium lines were recorded in the 312–334 nm UV region. The temporal evolution of plasma parameters such as excitation temperature and electron number density was evaluated. The effect of incident laser irradiance, position of the laser beam focal point with respect to the surface of illumination, single and double laser pulse effect on plasma parameters were also investigated. This study contributes to a better understanding of the LIBS plasma dynamics of the double laser pulse effect on the temporal evolution of various Ti emission lines, the detection sensitivity and the optimal dynamics of plasma for ionized states of Ti. The results demonstrate a faster decay of the continuum and spectral lines and a shorter plasma life time for the double pulse excitation scheme as compared with single laser pulse excitation. For double pulse excitation technique, the emissions of Ti lines intensities are enhanced by a factor of five which could help in the improvement of analytical performance of LIBS technique. In addition, this study proved that to avoid inhomogeneous effects in the laser produced plasma under high laser intensities, short delay times between the incident laser pulse and ICCD gate are required.     

Fixation of bioactive calcium alkali phosphate on Ti6Al4V implant material with femtosecond laser pulses

Bone implants made of metal, often titanium or the titanium alloy Ti6Al4V, need to be surface treated to become bioactive. This enables the formation of a firm and durable connection of the prosthesis with the living bone. We present a new method to uniformly cover Ti6Al4V with a thin layer of ceramics that imitates bone material. These calcium alkali phosphates, called GB14 and Ca10, are applied to the metal by dip coating of metal plates into an aqueous slurry containing the fine ceramic powder. The dried samples are illuminated with the 790 nm radiation of a pulsed femtosecond laser. If the laser fluence is set to a value just below the ablation threshold of the ceramic (ca. 0.4 J/cm²) the 30 fs laser pulses penetrate the partly transparent ceramic layer of 20-40 μm thickness. The remaining laser fluence at the ceramic-metal interface is still high enough to generate a thin metal melt layer leading to the ceramic fixation on the metal. The laser processing step is only possible because Ti6Al4V has a lower ablation threshold (between 0.1 and 0.15 J/cm²) than the ceramic material. After laser treatment in a fluence range between 0.1 and 0.4 J/cm², only the particles in contact with the metal withstand a post-laser treatment (ultrasonic cleaning). The non-irradiated rest of the layer is washed off. In this work, we present results of a successful ceramic fixation extending over larger areas. This is fundamental for future applications of arbitrarily shaped implants.     

Ablation mechanism study on metallic materials with a 10 ps laser under high fluence

Single shot ablation of metallic materials of aluminium, titanium alloy (Ti6Al4V) and gold has been studied with 10 picoseconds (ps) laser pulses experimentally and theoretically. The ablation rate variation at high fluence was explained by a simplified predictive model based on critical-point phase separation (CPPS) theory. A comparison between experimental and numerical results inferred that CPPS may well be the dominant ablation mechanism for high fluence laser ablation at 10 ps laser duration.     

Surface engineering of biomedical metallic materials by plasma-based low-energy ion implantation

Plasma-based low-energy ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, for surface engineering of metallic materials was emerged as low-temperature, low-pressure surface modification technique. Plasma source ion nitriding onto AISI 316L austenitic stainless steel produced a high nitrogen face-centered-cubic phase (γ_N) layer about 10 μm thick at the temperature of 380 °C during 4 h with the high microhardness of HK_0.1 N 22.0 GPa. The microhardness of the nitrided surface from the titanium nitride phase [(Ti, Al, V)N] layer on Ti6Al4V alloy at 750 °C during 4 h achieved up to about HK_0.1 N 15.5 GPa. No pitting corrosion in the Ringer’s solution at 37 °C was detected by electrochemical polarization measurement for the nitrided AISI 316L stainless steel and Ti6Al4V alloy, respectively. Plasma source ion nitriding of the metallic materials provided the engineering surfaces with combined improvement in hardness and corrosion resistance.     

Raman characterization of Ti–6Al–4V oxides and thermal history after kinetic friction

Raman spectroscopy is applied to study the surfaces of a pair of tantalum and titanium alloy samples after high-speed dry friction. The surface of titanium alloy (Ti–6Al–4V) shows titanium oxides on the rubbing surfaces. Raman spectra enable to differentiate the allotropic phases of anatase or rutile. The presence of these phases is the signature of the local thermal history during the friction tests. Moreover, Raman mapping allows localizing area the flash temperatures that may have been produced by the friction between sample asperities.     

Femtosecond laser-induced periodic surface structures on steel and titanium alloy for tribological applications

Laser-induced periodic surface structures (LIPSS, ripples) were generated on stainless steel (100Cr6) and titanium alloy (Ti6Al4V) surfaces upon irradiation with multiple femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas (5 × 5 mm²) covered homogeneously by the nanostructures. The irradiated surface regions were subjected to white light interference microscopy and scanning electron microscopy revealing spatial periods around 600 nm. The tribological performance of the nanostructured surface was characterized by reciprocal sliding against a ball of hardened steel in paraffin oil and in commercial engine oil as lubricants, followed by subsequent inspection of the wear tracks. For specific conditions, on the titanium alloy a significant reduction of the friction coefficient by a factor of more than two was observed on the laser-irradiated (LIPSS-covered) surface when compared to the non-irradiated one, indicating the potential benefit of laser surface structuring for tribological applications.     

Surface ablation by excimer laser irradiation of Ti and Ti6Al4V alloy

This paper presents the surface microstructure of Ti and Ti6Al4V alloy irradiated with a high output energy XeCl ( = 308 nm) excimer laser. The treatments are carried out on both materials at two beam fluences and the effects of single- and multiple-pulse irradiation are compared. The results of the scanning electron microscopy and of the X-ray diffraction techniques suggest the possible influence of both time-behaviour and energy fluence of the laser pulse on the relative weight of the ablation rate and of the reaction product deposition rate at the sample surface.     

Electrical discharge machining of titanium alloy (Ti-6Al-4V)

In this study, the electrical discharge machining (EDM) of titanium alloy (Ti-6Al-4V) with different electrode materials namely, graphite, electrolytic copper and aluminium and process parameters such as, pulse current and pulse duration were performed to explore the influence of EDM parameters on various aspects of the surface integrity of Ti6Al4V. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and hardness analysis were performed. The experimental results reveal that the value of material removal rate, surface roughness, electrode wear and average white layer thickness are tendency of increase with increasing current density and pulse duration. However, extremely long-pulse durations such as 200 μs led to decrease MRR and surface roughness. Furthermore, the surface hardness is increasing due to the Ti₂₄C₁₅ carbides formed on the surface and obvious cracks are always evident in re-solidified layer when machining copper electrode. The surface crack densities and critical crack lines were determined for the tested material. The graphite electrode is beneficial on material removal rate, electrode wear and surface crack density but relatively poorer surface finish.     

Enhanced fatigue performance of porous coated Ti6Al4V biomedical alloy

Biofunctional coatings are necessary to improve integration of titanium implants in the host tissue but they may be detrimental for the implant fatigue properties. This study presents an attempt towards enhancement of the in vitro fatigue strength of plasma electrolytic oxidation coated Ti6Al4V alloy by applying shot peening process prior to coating. The electrolytic oxidation was performed in calcium acetate and calcium glycerophosphate electrolytes that allowed formation of porous oxide coatings with high surface free energy and apatite like ability. A deformed surface layer coupled with induced residual compressive stresses seem to affect oxide growth rate and fatigue behavior of the titanium alloy.     

Study on bacteria adherence properties of Mo surface-modified layer in Ti6Al4V alloy prepared by plasma surface alloying technique

Mo surface-modified layer in Ti₆Al₄V alloy was prepared using plasma surface alloying technique. Microstructure of the modified layer was analyzed using X-ray photoelectron spectroscopy (XPS), rough-meter and GDA750 glow discharge optical emission spectrometer. Phase composition of the Mo surface-modified layer was characterized by D/max 2500 X-ray diffraction. Results show that the Mo surface-modified layers consist of pure Mo surface layer with 〈1 1 0〉 and 〈2 1 1〉 orientations and diffusion layer. Mo 3d, O 1s, C 1s and Ti 2p, O 1s, C 1s XPS spectra are recorded at topsurface in the Mo-modified layer and titanium substrate respectively. Because of the different roughness and microstructure, the Mo surface-modified layer can to some extent inhibit bacteria adherence.     

Structural characterization of titanium oxide layers prepared by plasma based ion implantation with oxygen on Ti6Al4V alloy

Ti6Al4V alloy was implanted with oxygen by using plasma based ion implantation (PBII) at pulsed voltage ranging from −10 to −50 kV with a frequency of 100 Hz. In order to maintain a lower implantation temperature, an oil cooling working table was employed. The structure of the modified layers was characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results show that the thickness of the titanium oxide layer increases significantly with the increase of implanted voltage. The structure of the modified layer changes along depth. It is found that the surface layer consists of TiO₂, and the subsurface layer is a mixing structure of TiO_2, Ti₂O₃ and TiO. There is crystalline rutile phase existing in the modified layer of sample implanted at high implanted voltage. In addition, in the outmost modified surface, aluminum present as oxidized state, and vanadium could not be detected.     

The Effect of Irradiation of a Titanium Alloy of the Ti–6Al–4V–Н System with Pulsed Electron Beams on Its Creep

Russian Physics Journal - Comparative studies of the effect of pulsed electron beam irradiation of the Ti–6Al–4V titanium alloys with the contents of hydrogen of 0.002 wt.% (VT6 alloy)...