Submerged arc welding is a welding method in which the arc burns under the flux layer. It has the advantages of stable welding quality,high production efficiency,no arc light,and less smoke. The performance of submerged arc welding joints depends on the welding process parameters. The process parameters of submerged arc welding have been summarized, including the influences of welding voltage,welding current,welding speed,welding wire diameter and welding flux,etc.,which can provide the reference for the improvement of the mechanical properties of welding joints.

Due to the intrinsic properties of larger-mismatched, stronger-polarization and non-equilibrium growth, the efficiency-droop effect has been a critical obstacle to improve the quantum efficiency of III-nitride short-wavelength LEDs under high current density. Quantum-Combined Stark Effect induced by built-in electric field existed within the active region of LEDs plays a key role to reduce the quantum efficiency and causes a redshift of luminous wavelength subsequently. In this study, the light output power, bandgap diagrams, radiative recombination efficiencies, carries concentrations, spontaneous emission properties and electrical properties of InGaN/AlGaN violet LEDs with different polarities (c-plane, m-plane and r-plane) at high current density of 600 A/m are investigated using APSYS software. Conclusions indicate that all the parameters of luminescence properties and electrical properties have strong dependence on the high current density of 600 A/m, which is contributive to eliminate the quantum-confined Stark effect and enhance the luminescence efficiency of polarity short-wavelength LEDs. The results of this paper provide theoretical bases for further optimizing and designing the active region and enhancing the luminous efficiency of short-wavelength LEDs.

An investigation into the mechanical properties of K55, N80, and P110 steels commonly used for casing drilling was carried out together with microstructural and fractographic analysis. The results show that P110 steel consisted of almost fully tempered martensite and exhibited a synergy combination of static tensile, dynamic impact, and fatigue crack propagation properties among the three steels, possessing a higher fatigue limit and deeper crack tolerance before failure occurred. The K55 steel consisted of the pearlite and network structure of ferrite and possessed a high strain hardening exponent and low impact property, which led to the more suitable application under incidental large overload and temperature change, but it was unsuitable under the condition of higher impact force. The properties of N80 steel were moderate, and its fatigue property was higher than that of K55 and lower than that of P110; its incidental overload resistance was also higher than that of P110. The casing drilling steel can be selected according to the environment.

图形化蓝宝石衬底(PSS)技术作为提高LED发光效率的方法之一,一直备受关注.研究了 PSS上生长的GaN薄膜的表面形貌、吸收光谱、红外光谱、拉曼散射(Raman)和太赫兹光谱等,并与常规蓝宝石衬底上的GaN外延薄膜进行对比.结果表明,PSS上生长的GaN外延薄膜的表面形貌、光提取效率(LEE)得到明显改善.此研究成果对进一步提高GaN基短波(蓝/紫光)发光二极管(LED)的发光效率具有一定的借鉴意义,为进一步拓展PSS器件的太赫兹响应提供了依据.

采用冲击试验及扫描电镜分析等方法研究了室温下试样厚度对U165和Q275结构钢夏比摆锤冲击吸收能量的影响.结果表明:相对较薄的试样不存在冲击载荷突降现象,但试样厚度为20 mm的Q275钢的冲击载荷突降高达80％以上;当试样厚度≤10 mm时,冲击吸收能量随试样厚度的增加总体呈线性变化,但不同材料冲击吸收能量随厚度变化的比例系数显著不同;当试样厚度>10 mm时,冲击吸收能量随厚度增加偏离了线性规律;此外,随着厚度的增加,不同材料冲击吸收能量的增量和断口形貌显著不同,这归因于材料的冲击韧性及其冲击断裂机制不同.对于厚度不满足标准试样的材料,标准试样的冲击吸收能量可通过测试不同厚度的非标试样,然后再用拟合公式计算得到.

采用冲击吸收能量法、剪切断面率法以及非剪切区颈缩比法对U165超高强度钻杆钢的韧脆转变温度进行了表征.结果表明:U165钻杆钢的韧脆转变温度约为1.8℃,高于1.8℃时,断裂模式逐渐变为韧性断裂,低于1.8℃时,断裂模式逐渐变为脆性断裂.非剪切区颈缩比法得到的试验钢的韧脆转变温度与冲击吸收能量法、剪切断面率法得到的基本一致,这说明非剪切区颈缩比法可用于表征试验钢的韧脆转变温度.3种方法相互结合,能够更有效地表征材料的韧脆转变温度.

In this article, the electrical properties of nMOSFET devices with different high- ${k}$ Al 2 O 3 capping layer thickness and TiN electrode have been systematically studied at deep cryogenic temperatures ranging from 10 to 300 K. The threshold voltage ${V}_{\text {TH}}$ , transconductance ${g}_{m}$ , carrier mobility $\mu $ , mobility attenuation factor $\theta $ , and subthreshold swing (SS) are extracted using the ${I}_{\text {DS}}$ – ${V}_{\text {GS}}$ curves and Y-function method at different temperatures. It is indicated that: 1) all the electrical parameters ( ${V}_{\text {TH}}$ , ${g}_{m}$ , $\mu $ , $\theta $ , and SS) show strong temperature dependence in the range of studied temperatures and 2) temperature-dependent electrical properties of nMOSFET devices will modulate at various cryogenic temperatures ascribed to the presence of the Al 2 O 3 capping layer on the SiO 2 dielectric layer, which increases the oxide trap density and consequentially adjusts the threshold voltage and mobility of the devices.

In this article, the interfacial properties of nMOSFETs with different thickness high- $\kappa $ Al 2 O 3 capping layer on an 8-nm SiO 2 and TiN gate stacks have been investigated using electrical measurement and low-frequency noise at room temperature. It is shown that the predominant 1/ ${f}$ noise is governed by the number fluctuations mechanism. It is indicated that: 1) presence of an Al 2 O 3 capping layer increases the noise power spectral density and, hence, the oxide trap density has an influence on the low-field mobility further and 2) effective work-function and the threshold voltage of nMOSFET should be modulated using the high- $\kappa $ Al 2 O 3 capping layers.

用OM、SEM、TEM及拉伸试验机等研究超高强度钢级钻杆N150及U165的显微组织和拉伸性能,并与高强钢级钻杆G105及S135进行对比.结果 表明:4种钻杆钢的显微组织均为回火索氏体组织,随钢级增加,显微组织更细小;抗拉强度增加速率低于屈服强度;屈服点应变与屈服强度正相关,抗拉强度点应变和抗拉强度负相关;静力拉伸能(STE)和静力韧度均单调增加,表明超高强度钻杆钢U165具有优良的综合拉伸性能;STE能较准确表征材料静态韧度.

本文介绍了双金属复合管的结构特点和主要生产工艺,对双金属复合管的失效形式及原因进行了详细的文献调研,整理了双金属复合管工艺和应用的发展现状,对双金属复合管的应用发展前景进行了展望.对其未来在制造和检测方面的发展趋势进行了分析,提出了应加快制造技术的研发和自动化程度,完善复合管无损检测技术,且标准规范需要系统化、规范化、全面化的建议.

借助静态液压万能试验机和低温试验箱,研究了钻杆钢在不同温度下的强度变化规律,同时用扫描电镜及透射电镜研究了钻杆钢的显微组织及拉伸断口形貌.结果 表明:随着温度的降低,钻杆钢的屈服强度和抗拉强度均呈增加趋势,屈强比呈下降趋势.随着钻杆钢级的提高,材料的抗拉强度温度敏感系数qb和屈服强度温度敏感系数qs均呈明显的减小趋势,但它们的比值呈明显的增加趋势.抗屈温度敏感系数比k(抗拉强度与屈服强度温度敏感系数比值)可用来表征温度对材料的力学性能的影响,k值越大,随着温度降低,相比屈服强度,抗拉强度提高更快,材料低温综合力学性能越好.在本文研究的温度范围内,随着温度的降低,钻杆钢的断口始终保持为延性断裂特征,这与材料塑性没有随温度降低而显著降低是一致的.

研究了U165超高强度钻杆钢的显微组织结构及其在低温环境下的拉伸性能,并对拉伸断口的宏观及微观形貌进行分析.结果 表明:U165超高强度钻杆钢的显微组织为回火索氏体,碳化物主要为(Cr,Fe)23C6;随温度的降低,该钢的屈服强度和抗拉强度均升高,相比之下,低温对该钢的抗拉强度具有更显著的影响;均匀伸长率、总伸长率以及断面收缩率对温度变化不敏感.

采用分子动力学模拟方法研究了在单轴拉伸载荷下,界面旋转角度和氢原子浓度对含有非对称倾斜Σ5晶界的双晶α-铁力学性能的影响.研究结果表明,双晶体的塑性变形主要是通过原始BCC相转变为亚稳态FCC相,再进而转变成新BCC相的过程来实现的,且该变形机制不依赖于氢原子的浓度.氢原子的引入使得双晶α-铁在塑性变形过程中,BCC-FCC的相变更容易发生,但在塑性变形后期氢原子阻碍了FCC相向BCC相的转变.此外,双晶α-铁的峰值应力随着氢浓度的增加而减小.

During the past two decades, GaN-based light-emitting diode has been used as a high-quality light-source. Low-frequency noise as a diagnostic tool for quality control and reliability estimation has been widely accepted and used for semiconductor devices. Understanding the origin of efficiency-droop effect is key to developing the ultimate solid-state light source. Various mechanisms that may cause this effect have been suggested, including carriers' escape, loses due to dislocations, and the Auger effect. In this study, we investigate the low-frequency noise behaviors of GaN-based blue light-emitting diode with InGaN/GaN multiple quantum wells. The measured currents range from 0.1 mA to 180 mA. According to the characteristics of power spectral density of current noise and the generation-combination mechanism between electrons and holes in the active region of light-emitting diode (LED), we adopt the well-known model of low-frequency noise to fit the relationship between power spectral density of current and frequency, and find that there exists a transition between generation-combination and 1/f noise when the light-emitting diode begins to work. In other words, it can be derived that the low-frequency noise behaviors are dominated by generation-combination noise when the currents are between 0.1 mA and 27 mA; with the current gradually increasing, the origin source of low-frequency noise in blue/violet-light LED will transit to the 1/f noise. Through the analysis of the transport and recombination mechanism of the carriers, and combination with the model of low-frequency noise, we analyze the corner frequency of the generation-recombination noise. The results of this paper provide an effective tool and method to study the conversion of light-emitting diodes.

借助SEM、TEM及冲击试验机等设备,研究了U165超高强度钻杆钢在不同温度下的冲击韧性.试验结果表明:随着温度降低到某一临界值,裂纹扩展阻力急剧下降,且随温度降低而减小.同时在小裂纹扩展阻力下,裂纹扩展的位移比例也随温度降低而增加,从而使得U165钻杆钢的冲击韧性急剧减小,对应的冲击断口呈现为显著的脆性特征,主要由解理结构组成.利用Boltzmann函数对U165钻杆钢的冲击能值进行拟合分析,韧脆转变温度约为1.8℃,但在较低温度下,依旧呈现出较高的冲击能值,约为40J,表明该材料韧脆转变温度适中,更适合于普通地区服役,同时也可在高寒地区服役.随着温度的降低,U165钻杆钢纤维区和剪切唇区减少,放射区增加,导致脆性特征明显.

The fatigue crack growth properties and tensile properties of three casing-drilling steels with different microstructures were conducted by scanning electron microscope,fatigue test machine,and universal test machine.The quantitative relationship of different parameters was built.The results show that the tempered martensite steel possessed significantly higher tensile strength and yield strength than ferrite-bainite-tempered martensite steel and pearlite-ferrite steel.Pearlite-ferrite steel had the maximum Paris constant m and minimum Paris constant C .Tempered martensite steel had minimum Paris constant m and the maximum Paris constant C . For steels with the same or similar chemical composition,Paris constant m decreased evidently with the increase of yield strength and Paris constant C decreased significantly with the increase of elongation.For different steels,Paris constant C increased with the decrease of paris constant m .The materials composition should be modified to obtain excellent combination properties when the tensile properties were improved to the critical value by means of heat treatment.

In this study we have investigated optical properties of GaN epilayer grown on cone -patterned and planar c-plane sapphire substrate by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) respectively. High-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscope (SEM), photoluminescence (PL) and Raman scattering measurements have been employed to study the crystal quality, surface morphology, optical properties and residual strain of GaN epifilms. Conclusions reveal that epitaxial films grown on patterned sapphire substrate can improve the crystal quality, enhance the surface morphology, and reduce the threading dislocation density. The mechanisms of growing on cone -patterned sapphire substrate to enhance the optical properties of GaN epifilms discussed from the viewpoint of residual strain state in this paper.

提升大学生的英语语言应用能力,尤其是听说能力,是大学阶段专业英语教学的重要目标.文章以专业英语中的听说教学方法为研究目标,探讨提高学生听说能力的策略,总结了专业英语听说词汇的特点,听说语法的特点及听说能力培养的方法,从而促使学生的专业英语听说水平得到最大限度的提高,实现国际学术交流能力的提升.

The effect of hydrogen on the mixed-mode Ⅰ /Ⅲ fracture toughness of casing-drilling steels was investigated by means of fatigue testers and SEM.The results show that hydrogen significantly brings down the ratio coefficient between the mode Ⅰ fracture toughness J Ⅰ and the mode Ⅲ fracture toughness JⅢ.This means,with increase of mode Ⅲ load,that the increase of JⅢ under the hydrogen pre-charging is less under the same decrease of J Ⅰ,so JT decreases.The decreases of three different microstructure casing-drilling steels J Ⅰ are remarkable.The inclusion can be obtained by extrapolation-extension method that JⅢ can be brought down by means of the hydrogen pre-charging,when the crack angle is 45°,that the decrease of tempered martensite steel(TM) steel J Ⅲ is the most remarkable.For the different microstructure steels,TM steel is the most sensitive to hydrogen,ferrite-bainite-martensite steel is in the middle,pearlite-ferrite steel is better for resisting hydrogen effect.Compared with uncharged hydrogen,the fracture surface of precharged hydrogen sample is remarkably flatter,which is consistent with a fact that its fracture toughness is the lowest.

本文以金属在电解质溶液中的腐蚀行为作为研究内容,结合溶液中腐蚀体系的基础理论——双电层模型的发展、演变、包容等特点,旨在帮助学生进一步理解溶液中腐蚀行为发生的物理与化学过程和离子运动的特点对电势,进而对腐蚀速率等因素的影响.本文提供了一种更加系统化、条理化的方式展现给学生,可提高教师的课堂授课质量,激发学生的学习兴趣.