Weld porosity in containers for storage of plutonium containing materials

Abstract

An autogenous gas tungsten arc closure weld was developed for the US Department of Energy's primary container for the storage of plutonium bearing materials. The occurrence of porosity at the tie-in point of the closure weld was investigated. The primary cause of the porosity was linked to the geometry at the root of the closure weld joint. The present paper describes the mechanistic model that was developed to describe and predict the porosity.     

Seam tracking based on estimation of weld position using Kalman filtering

Abstract

A seam tracking method is presented based on the estimation of weld position during the gas tungsten arc welding process. Kalman filtering of the weld pool images from a visual sensor is applied to compute recursively the solution to the weld position equations which are established based on an estimation of the centroid position of the weld pool images. This centroid, the position of which corresponds with the weld position, is extracted as the measurement eigenvector. The evolution of the weld position data from the weld pool images can be described through an appropriate process model, so that the weld position can be detected by applying a Kalman filter. This allows adjustment of the welding torch position in real time, which may significantly reduce processing time and promote seam tracking accuracy. Simulations and actual welding experiments have demonstrated the effectiveness of the proposed algorithm in the presence of weld pool image noise and have demonstrated the robustness of weld position detection for seam tracking.     

Influence of GMAW-P current waveforms on heat input and weld bead shape

Abstract

Manufacturers use different, proprietary pulse current programming algorithms in their synergic 'one knob control' pulsed gas metal arc welding (GMAW-P) power supplies. Since the different pulse waveforms produced by these supplies can produce somewhat different welding characteristics, inconsistent results can be obtained when transferring welding procedures between different GMAW-P power supplies. A primary objective of this work was to characterise the differences in welding heat input and weld bead shape that could be produced by the pulsed current waveforms from four different commercial supplies. To eliminate the affects of subtle differences in electrical characteristics and to ensure that the exact shape of all waveforms was fully known, the comparison was also done by simulating the waveforms generated by three of the four power supplies on the fourth supply, which was equipped with waveform programming capability. Then, the four waveforms were used to create 'bead on plate' welds over a range of wire feed speed settings, and corresponding heat inputs were calculated from current and voltage samples recorded by a computer data acquisition system during welding. Welds were also done at the same wire feed speed setting using a constant voltage supply. All welds were then cross-sectioned for penetration and dilution measurements. In general, all of the waveforms produced good metal transfer and weld quality. However, the heat input and beads shapes varied noticeably. The heat inputs for the four pulse waveforms and constant voltage welds differed by as much as 150 J mm^?1 (17% of the maximum heat input) at the highest wire feed speed of 212 mm s^?1. The weld penetration differed by 1 mm (22% of the maximum penetration) at a wire feed speed of 169 mm s^?1 and the dilution differed a maximum value of 6.5% dilution (22% of the maximum dilution) at a wire feed speed of 169 mm s^?1 .     

基于电磁压制的Ag-Cu-Ge钎料合金成形工艺

针对Ag-Cu-Ge系钎料难以加工成薄片的难题,利用电磁粉末压制结合液相烧结的成形工艺制备了钎料薄片,探究了不同压制电压及烧结温度对钎料薄片致密度和组织结构的影响,选用优化工艺下的钎料薄片对铜板进行焊接实验。实验结果表明:压坯致密度随着压制电压的提高而显著提升,当压制电压为2800 V时,压坯致密度达到最大值88.62%,而电压升高到3000 V时,锗粉颗粒内部开始产生裂纹甚至破裂;250℃烧结温度下烧结体出现了弹性后效现象,当烧结温度升高到400℃时,烧结体致密度增长率达到最大值2.63%,若温度继续升高,烧结体晶粒则出现粗化现象;最终当焊接温度为600℃时,焊缝组织均匀,与母材形成了较好的冶金结合,表现出良好的焊接性能,说明了该成形工艺用于制备钎料薄片的可行性。     

Ti-Zr-Ni-Cu非晶钎料在Si3N4陶瓷上的润湿性研究

针对Si3N4陶瓷的高温活性钎焊要求,设计了高温Ti-Zr-Ni-Cu非晶钎料成分,并采用单辊急冷法成功制备了Ti-Zr-Ni-Cu非晶钎料.对比分析了相同成分的Ti-Zr-Ni-Cu非晶和晶态钎料在Si3N4陶瓷表面的润湿情况.结果表明:在低真空条件下,晶态钎料能够润湿Si3N4陶瓷,非晶钎料却因完全氧化而失效.在5×10-3Pa高真空条件下,非晶钎料的润湿性优于晶态钎料,在研究的Ti-Zr-Ni-Cu非晶钎料中,Ti40Zr25Ni15Cu20非晶钎料对Si3N4陶瓷的润湿性最佳.     

晶化温度对非晶态Cr-Fe-C合金镀层的影响

采用三价铬电镀液,在4Cr10Si2Mo钢工件表面电沉积非晶态Cr-Fe-C合金镀层.通过改变络合剂的含量、电流密度和电镀时间,在阴极上沉积了不同厚度的非晶态Cr-Fe-C层.用扫描电子显微镜和光学显微镜、X射线衍射仪、能谱仪测定、显微硬度计研究了从三价铬镀液中电沉积Cr-Fe-C镀层的工艺以及镀层的形貌、结构与性能.结果表明,利用该工艺获得了厚度为30 μm、27 wt%Fe的非晶态Cr-Fe-C合金镀层.该镀层耐蚀性较好,经600℃×1 h晶化处理后硬度最高可达1 800 HV0.05.     

非晶态合金薄膜铜衬底超精密抛光的实验研究

本文采用聚氨酯抛光盘和绒布抛光垫对铜衬底进行超精密抛光工艺研究,对铜衬底的表面粗糙度、材料去除率以及铜衬底表面组织结构变化过程进行了研究,并讨论了铜衬底在超精密抛光时,不同抛光条件对其表面粗糙度和材料去除率的影响,以及抛光压力对铜衬底的表面形成过程的影响。结果表明,采用聚氨酯抛光盘和绒布抛光垫可以消除划痕,抛光后的铜衬底表面粗糙度可达Ra6 nm。     

基于正交回归的GH44合金本构关系研究

通过热物理模拟试验，系统地研究了主要热力参数(变形温度、变形速率、变形程度)与流动应力间的数值关系，采用正交设计原理，科学地分析并回归出GH44合金的本构方程，定性地探讨热力参数对GH44合金成形性能的影响规律，为GH44合金的热变形数值模拟和热力参数的合理制定与控制提供了依据。     

工艺参数对激光金属沉积铜钛合金复合材料的影响

为获得最佳设计方案,设计两种实验方案,通过改变工艺参数对铜钛合金复合材料进行激光金属沉积。从显微组织演变、硬度和力学性能三方面对所沉积的复合材料进行表征。结果表明：复合材料的显微组织由一次、二次和三次枝晶臂,针状组织和α+β共晶组织组成。两种实验方案结果表明,在激光功率为1200 W、扫描速率为1.2 m/min的条件下得到的样品E具有最高的硬度,其值为HV (190±42),但由于其脆性,因此出现一些横间裂纹;而在激光功率为1200 W、扫描速率为0.3 m/min条件下得到的样品B无裂纹产生,且其显微组织良好并含有较多的枝晶。得到的铜复合材料的应变硬化系数为3.35。     

Influence of annealing treatment on properties and microstructures of alumina dispersion strengthened copper alloy

Alumina dispersion strengthened copper(ADSC) alloy was produced by internal oxidation. The hardness, ultimate tensile strength and electrical conductivity measurements and microstructure observation on the produced 0.12?SC (0.24% Al2O3, mass fraction) and 0.25% ADSC (0.50% Al2O3) subjected to different annealing treatments were conducted. The results show that the microstructure of the produced ADSC is characterized by an uniform distribution of nano-Al2O3 particles in Cu-matrix; the particles range in size from 20 to 50 nm with an interparticle spacing of 30 - 100 nm. The produced 0.12% ADSC can maintain more than 87% hardness retention after 900℃, 1 h annealing treatment; the recrystallization can be largely retarded and is not fully completed even after annealing at 1 000℃ for 1 h, followed by cold deformation of 84% ; local grain growth can be observed after 1 050℃ ,1 h annealing treatment. The results also show that increasing either the alumina content or cold deformation degree increases the hardness of the produced ADSC.     

热处理对铁基非晶合金涂层相组成及磨损性能的影响

采用超音速火焰喷涂技术在0Cr13Ni5Mo不锈钢基体上制备了铁基非晶涂层,研究了500%～800℃不同温度热处理对涂层的相组成和摩擦磨损性能的影响.从涂层的显微硬度分析、相组成分析、晶粒大小分析、以及摩擦磨损试验分析表明:随着热处理温度升高涂层的相结构及性能发生变化,在600℃时,涂层中析出大量的纳米硬质相,涂层的显微硬度和耐磨损性能也随之大幅提高;涂层的显微硬度在600℃时达到最大,耐磨性能在750℃时最好.     

Influence of diffusion bonding conditions on bonding strength of damping copper alloy to stainless steel

The experimental investigation of different tran sition metals was carried out in the diffusion bonding joints of Cu alloys (CuAlBe) to stainless stee l (1Cr18Ni9Ti). The microstructure of the joint was analyzed with microscopic examination, SEM, EPMA and X-ray diffraction. Following conclusions have been draw n: (1) The joint strength with the Ni interlayer was higher than that with Cu in terlayer when the welding parameters were same;(2)When Ni interlayer was thinner ,Al could interact with Ni and Fe,and the intermetallic compounds,such as Fe3A letc,were formed in the interface,which decreased the strength of the joints;(3 ) When the bonding temperature was higher,because of the diffusion of Cu in Ni being faster than Ni in Cu,a Kirkendall effect was produced,which also decreased the strength of the joints.     

Superplastic solid state welding of steel and copper alloy based on laser quenching of steel surface

1　INTRODUCTIONThe copper and copper alloys possess a num ber of superior properties, such as excellent elec trical conductivity, excellent thermal conductivityand forming property, so the complex componentsof the steel, copper and copper alloy have comple mentary advantages on the economy and perform ance[1, 2]. But it is very difficult to realize the goodbonding of them by adopting routine fusion weld ing and braze because of a rather large difference inthe melting point, coefficient…     

Influence of the borohydride concentration on the composition of the amorphous Fe–B alloy produced by chemical reduction of synthetic, nano-sized iron-oxide particles: Part I: Hematite

Amorphous Fe–B alloys can be prepared at room temperature by reduction with borohydride of iron-oxide particles in suspension. By varying the borohydride concentration, amorphous Fe–B alloys with boron contents between 2 and 13 at.% have been produced by reduction of synthetic (nano-sized particles) and natural (micro-sized) hematite (α-Fe₂O₃) using sodium borohydride (NaBH₄). The results presented in this paper were obtained from a systematic study of the effect of borohydride concentration on the resulting reaction products using a variety of experimental techniques, such as X-ray diffraction, wet chemical analyses, thermal analyses, scanning electron microscopy, transmission Mössbauer spectroscopy (TMS) and integral low-energy electron Mössbauer spectroscopy (ILEEMS). Three distinct NaBH₄ concentrations have been applied. Beside unreacted hematite, amorphous Fe_1−xB_x alloys have been identified from the TMS spectra recorded at various temperatures between 15 K and room temperature. The amount of Fe_1−xB_x increases strongly with increasing NaBH₄ concentration, and for a given concentration with increasing specific surface area (SSA). Thermal analyses have suggested that for any given reduction condition, the boron content x in the formed amorphous alloy has a bimodal distribution. This is found to be consistent with the finding that the contribution of the Fe_1−xB_x phase to the total Mössbauer spectra consists of a superposition of a broad sextet and doublet. ILEEMS has further revealed that especially the surface layers of the hematite grains are affected by the reduction processes.