Observation of residual stress and defects in silicon induced by scribing

Residual stresses induced by three scribing methods, diamond point scriber, laser scriber and diamond blade saw, are studied quantitatively by infra-red photoelasticity. It is clear that diamond blade saw scribing is most desirable, for residual stress induced by it is several times smaller than the stress caused by the other methods. The stress gradient differs between the laser scribed sample and the others, probably because of the difference in stress generation mechanism. Removing the damaged layer by etching reduces residual stress. The three scribing methods are also studied by the observation of defects after annealing and the results are compared with those determined by photoelastic measurement.     

Molecular Dynamics Simulation of Porous Layer-enhanced Dislocation Emission and Crack Propagation in Iron Crystal

The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e.g. when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking (SCC). Molecular dynamics (MD) simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity KI, or stress. To respond to the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity KI, resulting in SCC.     

Effects of annealing on the damage morphologies in BF 2 + ion implanted (1 0 0) silicon

The effects of annealing on the damage morphologies and impurity redistributions in BF ₂ ⁺ ion implanted (1 0 0) silicon were studied using secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM) and Rutherford backscattering (RBS) ion beam channelling technique. An amorphized silicon layer and a heavily-damaged crystal layer containing a high density of point-defect clusters, are formed on the silicon wafer by the ion implantation. SIMS depth profiles of both boron and fluorine are almost Gaussian distribution. Both furnace annealing and rapid thermal annealing cause recrystallization of the amorphized layer and formation of dislocation loop bands out of the point defects. SIMS depth profiles for both impurities show anomalous double peaks at the same depths. These facts suggest that the primary peak is due to the peak of the Gaussian distribution and the secondary peak due to the gettering effects of residual dislocation loop band.     

The structural characteristics of radiation damage produced by high energy (2.7 MeV) ion implantation in GaAs

The radiation damage induced by the implantation of 2.7 MeV P⁺ and N⁺ ions with a dose of 6.4 × 10¹⁶ ions cm^–3 into GaAs at room temperature has been studied by transmission electron microscopy. The as-implanted material was found to consist of a buried amorphous layer which was sandwiched between a heavily damaged but crystalline cover layer exhibiting a high density of black dot defects, microtwins and dislocation loops and a less damaged substrate region. Post-implantation annealing of the specimens at 250° C for 6 h resulted in the recrystallization of the amorphous and cover layers by random nucleation of grains producing a polycrystalline region on the single crystal substrate. However, a second stage annealing of these samples at 400° C for 2 h caused an epitaxial regrowth of the implanted layer on the undamaged substrate producing single crystal regions which were heavily twinned on all {111} planes. The results of the present microstructural analyses have been compared with the previous infra-red reflectivity studies on identically implanted GaAs samples to determine the effects of structural changes on the dielectric properties. The two studies are found to be in reasonable agreement. The present results are also compared with those from previous lower energy-lower dose implantations.     

Rafting-Enabled Recovery Avoids Recrystallization in 3D-Printing-Repaired Single-Crystal Superalloys

The repair of damaged Ni-based superalloy single-crystal turbine blades has been a long-standing challenge. Additive manufacturing by an electron beam is promising to this end, but there is a formidable obstacle: either the residual stress and γ/γ ′ microstructure in the single-crystalline fusion zone after e-beam melting are unacceptable (e.g., prone to cracking), or, after solutionizing heat treatment, recrystallization occurs, bringing forth new grains that degrade the high-temperature creep properties. Here, a post-3D printing recovery protocol is designed that eliminates the driving force for recrystallization, namely, the stored energy associated with the high retained dislocation density, prior to standard solution treatment and aging. The post-electron-beam-melting, pre-solutionizing recovery via sub-solvus annealing is rendered possible by the rafting (i.e., directional coarsening) of γ ′ particles that facilitates dislocation rearrangement and annihilation. The rafted microstructure is removed in subsequent solution treatment, leaving behind a damage-free and residual-stress-free single crystal with uniform γ ′ precipitates indistinguishable from the rest of the turbine blade. This discovery offers a practical means to keep 3D-printed single crystals from cracking due to unrelieved residual stress, or stress-relieved but recrystallizing into a polycrystalline microstructure, paving the way for additive manufacturing to repair, restore, and reshape any superalloy single-crystal product.     

Factors affecting surface quality in diamond turning of oxygen-free high-conductance copper

In identical cutting conditions, it has been shown that the surface quality of ultraprecisely machined oxygen-free high-conductance copper samples, for which a single-point diamond tool is used, depends on the microstructure and properties of the materials, as well as the processing sequence. It has been found that samples subjected to colddeformation-recrystallization annealing have the best surface quality after being diamond turned. In addition, crystal uniformity and the processing sequence affect the roughness and residual stress of the finished surface.     

Dislocation Mechanism of Diamond Crystal Growth from Fe—Ni—C System at High Temperature—High Pressure

Some dislocations,which are generated in the diamond single crystal during the diamond crystal growth from Fe-Ni-C system,may affect diamond crystal growth mode at high temperature-high pressure(HPHT). The concentric dislocation loops were successfully examined by Moire images.The surface morphologies of growing and as-grown diamond single crystals were observed by scanning electron microscopy(SEM).The concentric dislocation loops formation process and their effect on the diamond crystal growth mode were analyzed.It should be noted that whatever the nature of the dislocation is ,should the Burgers vector of dislocation has a component at the direction normal to the growth interface,the dislocation will make the face parallel to the growth interface grow into spiral face.The presence of consecutive spiral steps on the diamond crystal surface also provides a direct evidence of the dislocation mechanism of diamond crystal growth.     

激光冲击处理对金属微结构及其性能的影响

论述了激光冲击处理的基本原理,分析了激光诱发的冲击波在材料中的传播过程.激光冲击处理会使金属材料表层发生塑性变形而产生很高的残余压应力;冲击区的显微组织中会产生高密度位错,有时亦有孪晶与相变产生;金属材料表层的塑性变形、高残余压应力、高密度位错、孪晶以及相变,这些因素的共同作用使得金属材料表面硬度、疲劳寿命获得很大的提高.     

High-temperature Raman study in CVD diamond

Measurements of the Raman spectra in chemical vapour deposition (CVD) diamond films at temperatures up to 1200 K are presented. Specifically, the evolution of Raman line position, line width, and intensity were monitored as a function of heating time. The red shifting and the line width broadening of CVD diamond's Raman line with temperature are very similar to that of natural diamond's. However, the detailed temperature dependence of Raman line width depends on the orientation of the CVD diamond crystal and the ambient gas used during thermal treatment. Since the CVD diamond usually exhibited a broader Raman spectra than natural diamond, the evolution of the line width upon heating is thus expected to depend on the origins and the annealing effects of the residual stress. For (111) CVD diamond subjected to annealing in air at 973 K, the line width decreased by more than one wavenumber while the line intensity increased by more than an order of magnitude before it decreased subsequently. In contrast, there is hardly any observable changes of the line width for (100) CVD diamond heated in air at 1173 K. Measurements conducted in He versus in air suggested that the reduction of the non-diamond carbon phase (therefore, the reduction of stress) is likely due to oxidation, which occurs more readily in (111) than in (100).     

A mechanism study on characteristic curve of residual stress field in Ti–6Al–4V induced by wet peening treatment

The microstructure evolution of Ti–6Al–4V alloy induced by wet peening treatment was studied in this work. The results show that the dislocation interaction dominates the grain refinement process. The modified layer could be divided into reconfiguration regime, unstable regime and metastable regime with depth. Corresponding to the characteristic curve of residual stress field, the maximum of compressive residual stress locates in the unstable regime and the dislocation annihilation and rearrangement lead to the decrease of the compressive residual stress in the near surface layer.     

Effects of annealing on propagation in ion-implanted contiguous-disk bubble devices

Bubble propagation margins are found to be affected by heat treatment in ion-implanted contiguous-disk devices fabricated on liquid-phase epitaxial (LPE) grown double-layer garnet films which support 1-μm bubbles. When an optical reflector is deposited directly on the driving layer interfacial diffusion takes place, and this raises the coercivity of the implanted layer, which in turn causes a severe degradation of propagation margins. In samples fabricated with optical reflectors isolated from the driving layer, the adverse effects of annealing on propagation margins are stronger in close-packed minor loops due to interaction of long-range charged walls as compared with isolated loops and isolated disks, and they cease to propagate bubbles after annealing in the temperature range of 350-400°C, whereas the loss of margins in the isolated loops and disks are typically less than 30 percent after 600-650°C annealing treatments. Stress gradients caused by the discontinuity in the overlay patterns contribute significantly to the increase of threshold drive field after anealing. The rapid degradation of propagation margins found after annealing in the temperature range of 350-400°C in all samples is caused by reordering of the damaged lattice.     

Interfacial structure, residual stress and adhesion of diamond coatings deposited on titanium

The interfacial structures of diamond coatings deposited on pure titanium substrate were analyzed using scanning electron microscopy and grazing incidence X-ray diffraction. Results showed that beneath the diamond coating, there was one titanium carbide and hydride interlayer, followed by a heat-affected and carbon/hydrogen diffused Ti layer. Residual stress in the diamond coating and TiC interlayer under different process parameters were measured using Raman and X-ray diffraction (XRD) methods. Diamond coatings showed large compressive stress on the order of a few giga Pascal. XRD analysis also showed the presence of compressive stress in the TiC interlayer and tensile stress in the Ti substrate. With increasing deposition duration, or decreasing plasma power and concentration of CH₄ in gas mixture, the compressive residual stress in the diamond coating decreased. The large residual stress in the diamond coating resulted in poor adhesion of the coatings to substrate, but adhesion was also related to other factors, such as the thickness and nature of the TiC interlayer, etc. A graded interlayer design was proposed to lower the thermal stress, modify the interfacial structure and improve the adhesion strength.     

高品质油田钻探用PDC热残余应力分析与优化设计

为解决平界面结构PDC因残余应力而引起的强度问题,在研究PDC热残余应力分布规律的基础上,结合非平面连接技术与梯度过渡技术,设计并研制了新型内置过渡层结构复合片.数值计算结果表明:该复合片聚晶金刚石层(PCD)表面拉应力区明显减弱,其中,轴向最大拉应力为126 MPa,仅为平面界面结构PDC的13.2%,而PCD层上表面的径向拉应力和外侧面的轴向拉应力分别比平界面结构PDC降低了82.5%和94.2%.该复合片磨耗比达到16.43×104,平均抗冲击强度达到472 J,现场钻探实验同样证明了该复合片的优异使用性能.     

The effects of residual stress on fatigue behavior and crack propagation from laser shock processing-worked hole

Laser shock processing (LSP) is used to enhance the fatigue behavior of the structures. The effects of residual stress on fatigue behavior and crack propagation from LSP-worked hole were performed in this investigation. The influence of compressive stress on fatigue behavior and crack propagation of the hole was revealed, and a parametric study on residual stress and stress intensity factor was performed in order to determine their effect on crack growth propagation. The dislocation microstructure of 7050 aluminum at different laser intensities shows similar results, which indicated that LSP had an obvious inhibitory action to fatigue crack initiation and growth of the hole crack.     

金刚石刀具单点切削单晶硅加工表面特性

本文利用超精密机床对单晶硅进行了斜切及车削实验,采用拉曼光谱仪测量单晶硅材料切削表面的损伤,利用高斯和洛伦兹分布拟合拉曼光谱得到单晶硅表面相变层厚度及残余应力信息．结果表明,单晶硅切削表面与磨削、纳米划擦表面不同,除了非晶相外,测不到其他高压相．随着切削厚度的增大,单晶硅表面非晶层的厚度和表层的残余应力也会相应增加．较大的切削厚度使得残余应力变得不均匀,最终导致单晶峰退简并分裂成2个或3个峰．一般单晶硅的塑性车削生成表面由于切削厚度相对较小,其表面非晶层相对较薄,表面存在轻微残余压应力．当车削生成表面的切削厚度较大时,表面有脆性凹坑,非晶层相对较厚,残余压应力较大．车削过程是对已加工表面的切削,由于已加工表面非晶硅的存在,采用较高的切削速度可以增加切削区域温度,提高单晶硅表面非晶层的塑性,可加工出更好的光学表面．     

Alteration of internal stresses in SiO2/Cu/TiN thin films by X-ray and synchrotron radiation due to heat treatment

A break of wiring by stress-migration becomes a problem with an integrated circuit such as LSI. The present study investigates residual stress in SiO₂/Cu/TiN film deposited on glass substrates. A TiN layer, as an undercoat, was first deposited on the substrate by arc ion plating and then Cu and SiO₂ layers were deposited by plasma coating. The crystal structure and the residual stress in the deposited multi-layer film were investigated using in-lab. X-ray equipment and a synchrotron radiation device that emits ultra-high-intensity X-rays. It was found that the SiO₂ film was amorphous and both the Cu and TiN films had a strong {1 1 1} orientation. The Cu and TiN layers in the multi thick (Cu and TiN:1.0 μm)-layer film and multi thin (0.1 μm)-layer film exhibited tensile residual stresses. Both tensile residual stresses in the multi thin-layer film are larger than the multi thick-layer film. After annealing at 400 °C, these tensile residual stresses in both the films increased with increasing the annealing temperature. Surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat-treatment.     

Observations on the fracture and deformation behaviour during annealing of residually stressed polycrystalline aluminium oxides

Highly residually stressed polycrystalline aluminium oxides were found to exhibit residual stress relaxation, as evidenced by changes in load-bearing ability, at temperatures as low as about 850° C. This temperature is much too low for such relaxation to occur by dislocation, Nabarro—Herring or Coble creep. Irreversible changes in specimen dimension coupled with SEM-fractography revealed that the stress relaxation resulted from creep by intergranular cavitation and crack propagation. In one aluminium oxide, such cavitation and crack propagation appeared to take place in a stable mode along a viscous glassy grain boundary phase. In high-purity fine-grained aluminium oxide, crack propagation occurred in a frequently totally catastrophic and highly unstable manner. This latter material was also observed to exhibit spontaneous fatigue during isothermal anneal. Implications of the findings of this study for the use of thermal anneals to promote residual stress relaxation in structural ceramic materials are discussed.     

Residual stress, Young''s modulus and fracture stress of hot flame deposited diamond

Chemical vapour deposition (CVD) diamond coatings deposited on various substrates usually contain residual stresses. Since the residual stress affects the adhesion of the coating to the substrate, as well as the performance of the coating/substrate composite in many technical applications it is of importance to study the magnitude of these stresses.

In the present study the hot flame method was used to deposit diamond coatings on cemented carbide inserts by scanning the surface with a nine flame nozzle. By varying the oxygen to acetylene flow ratio and the deposition time coatings of different qualities and thicknesses were obtained. The residual strain/stress of the coatings was measured by three different methods: X-ray diffraction using the sin² (Ψ) method, Raman spectroscopy and disc deflection measurements. To extract the residual stress from the strain data the Young's modulus was obtained from bending tests of diamond cantilever beams manufactured from free standing diamond films. The latter technique was also used to determine the fracture stress of the diamond films.

All deposited coatings displayed a residual compressive strain/stress state. The residual strain in the diamond coatings did not vary with coating thickness (1.5 μm to 20 μm) but was found to increase from −1.8 × 10⁻³ to −2.2 × 10⁻³ with decreasing diamond quality. The compressive residual stress was found to decrease from −2 GPa to −1.3 GPa with decreasing diamond quality. This is mainly due to a decrease in Young's modulus (from 1.1 TPa to 0.6 TPa) with decreasing diamond quality. Also the fracture stress was found to decrease (from 1.8 GPa to 0.8 GPa) with decreasing diamond quality. The three methods used for measuring the stress state in the coatings, X-ray diffraction, Raman spectroscopy and deflection measurement, all give the same result. The deflection technique has the advantage that no information about the elastic properties of the coating is needed, whereas Raman spectroscopy has the best lateral resolution (≈5 μm) and is the fastest method (≈5 min).     

Preparation and optimization of freestanding GaN using low-temperature GaN layer

In this work, a method to acquire freestanding GaN by using low temperature (LT)-GaN layer was put forward. To obtain porous structure and increase the crystallinity, LT-GaN layers were annealed at high temperature. The morphology of LT-GaN layers with different thickness and annealing temperature before and after annealing was analyzed. Comparison of GaN films using different LT-GaN layers was made to acquire optimal LT-GaN process. According to HRXRD and Raman results, GaN grown on 800 nm LT-GaN layer which was annealed at 1090 °C has good crystal quality and small stress. The GaN film was successfully separated from the substrate after cooling down. The self-separation mechanism of this method was discussed. Cross-sectional EBSD mapping measurements were carried out to investigate the effect of LT-buffer layer on improvement of crystal quality and stress relief. The optical property of the obtained freestanding GaN film was also determined by PL measurement.     

Residual stress in CIGS thin film solar cells on polyimide: simulation and experiments

Sputtering technique is used to prepare Cu(In,Ga)Se₂ (CIGS) thin film solar cells on a UPILEX-S 50S polyimide substrate in order to investigate the residual stress in the Mo back contact and CIGS absorber layer after selenized annealing with various the thickness ratios of the Mo contact, R_Mo. A comparison between the results of numerical simulation and those obtained from X-ray diffractometry, indicate the existence of compressive residual stress in both the Mo contact and the CIGS absorber layer. The residual stress in the Mo contact was inversely proportional to the residual stress in the CIGS absorber layer. Residual stress decreased with an increase in the thickness ratio of the Mo contact. The empirical formulae for the residual stresses as a function of R_Mo in the Mo and CIGS films were deduced, from the results of this study.