为阐明异种钢激光填丝焊接工艺参数对焊缝成形的影响, 以不等厚板2 mm 45钢和6 mm 316L不锈钢为试验材料, 采用激光填丝焊接方法进行焊接, 研究不同对接间隙下的焊缝成形以及焊接接头的力学性能。结果表明, 随着对接间隙的增加, 余高逐渐减小, 焊缝形貌从钉子形向H形过渡, 随着对接间隙变大, 焊缝形成缺陷。焊缝中心硬度随着对接间隙的增加而减小, 焊接接头硬度最高处位于45钢热影响区。焊接接头的抗拉强度随着对接间隙的增加先增大后减小。在对接间隙为0.6 mm时, 表面形貌良好且抗拉强度最高, 焊接试验断裂位置在2 mm 45钢一侧。

为研究铜渣尾矿作为填料对沥青混合料性能的影响, 分析了铜渣尾矿的物理化学性质, 通过马歇尔稳定度试验确定沥青混合料的最佳配合比, 开展车辙试验、劈裂试验、冻融劈裂试验、浸水马歇尔试验来评价沥青混合料的路用性能, 对铜渣尾矿沥青路面进行检测, 并通过微观形貌分析铜渣尾矿与沥青的黏附特征。结果表明: AC-25C、AC-20C、AC-16C、AC-13C沥青混合料中铜渣尾矿掺量分别为4%、3%、3%、2%(质量分数), 其对应沥青用量为38%、4.2%、4.5%、4.6%(质量分数)时, 沥青混合料性能最佳。与石灰石沥青混合料相比, 铜渣尾矿沥青混合料的高温稳定性、抗裂性、水稳定性得到明显的提升。铜渣尾矿沥青路面性能良好, 其渗水系数为62 mL/min, 摩擦系数为90, 压实度为964%, 均符合规范标准, 铜渣尾矿与沥青形成的沥青胶浆具有良好的黏结性能。

采用 AgCu钎料瞬时液相扩散连接 SiBCN陶瓷和 Ti2AlNb合金, 研究连接温度和时间对接头微观组织和力学性能的影响。结果表明: 连接过程中, Ti2AlNb合金中的 Ti元素向 AgCu液相中溶解并与 SiBCN陶瓷反应产生 TiC界面反应层；液相中的Cu元素则向 Ti2AlNb中扩散形成 Nb(s, s)和 TiCu2Al, 使得液相发生等温凝固。随着温度升高或保温时间的延长, TiC层厚度增加, Cu(s, s)消失而 TiCu2Al化合物含量增加, 接头室温抗剪强度呈现先上升、后下降趋势。在 840℃保温 40 min时所获接头在室温和500℃时抗剪强度分别达到 (73±10) MPa和(95±16) MPa, 这得益于 Ag(s, s)良好的耐热性和应力缓解效果。

为模拟钢轨缺口、裂纹缺陷修复，在U75V钢轨母材上开设U形坡口进行激光填丝焊接修复，获得的优化修复工艺参数为：激光功率P=5 000 W，焊接速度500 mm/min，送丝速度200 cm/min，离焦量+20 mm，Z轴抬升0.75 mm/道。焊后的焊缝热影响区存在针状马氏体组织，再经过600 ℃保温1 h的高温回火处理后，针状马氏体转变为回火索氏体组织，回火后焊缝抗拉强度及硬度与母材接近，摩擦因数略高于母材，但仍满足实际工况要求。

以Ag-CuO-B2O3为钎料, 采用空气反应钎焊法连接了Al2O3陶瓷, 在接头中合成了新型Cu2Al6B4O17晶须。研究了连接温度与保温时间对接头显微结构、性能以及生成的晶须结构的影响。结果表明: 钎焊过程中, Al2O3与钎料中的CuO、B2O3发生反应生成Cu2Al6B4O17晶须, 获得性能优异的可靠接头。保温时间为60 min、连接温度高于950 ℃时, 可以实现Al2O3陶瓷接头的有效连接, 钎缝中心区主要为Ag, 靠近连接界面处为CuO、Cu3B2O6相及Cu2Al6B4O17晶须。随着连接温度的升高, 接头的抗剪强度升高。连接温度高于1 050 ℃后, 晶须变得粗大, 出现黏接, 对接头的强化效果减弱, 接头的抗剪强度降低。连接温度高于1 100 ℃后, 晶须分解为片层状产物, 接头的抗剪强度大幅降低。最佳工艺参数为在1 000 ℃条件下保温60 min, 接头的抗剪强度可达86.7 MPa, 断裂发生在焊缝中靠近母材处。

磷石膏(PG)是磷酸湿法工艺中产生的固体废渣, 大量堆存造成环境污染。PG经球磨和煅烧处理得到的无水磷石膏(APG)再经表面疏水改性后可用作高分子材料的填料, 在材料中起到增韧、增强作用, 提高材料的综合力学性能, 成为PG资源化利用的一种有效途径。以APG为主要原料, 以活化指数为响应值, 通过单因素试验和响应面法对APG疏水改性工艺条件进行优化。结果表明, 响应曲面建立的数学模型拟合度较高, NaOH浓度、KH570添加量和反应时间3个因素对活化指数均有显著影响, 其中KH570添加量是影响改性效果的主要因素。APG最优疏水改性条件为: NaOH浓度2.6 mol/L, KH570添加量3.10 g, 反应时间149 min。最优条件下改性APG的活化指数为0.968 9, 接触角为84.51°。

A phase-field model is developed in this paper based on the similarity between mechanical fracture and dielectric breakdown. Electrical treeing is associated with the dielectric breakdown in solid dielectrics by the application of high voltages. Instead of explicitly tracing the propagation of conductive channel, this model initializes a continuous phase field to characterize the extent of damage. So far, limited research has been conducted for simulating the effect of nanofiller dispersion on electrical treeing. No study has modeled the effect of uniform and nonuniform dispersion of nanofillers with varying filler concentration on treeing. Since electrical treeing tends to decrease the breakdown strength of solid dielectrics therefore, nanofillers are widely used to distract the tree from a straight channel to distribute its energy in multiple paths. Diverting a straight treeing channel into multiple paths reduces the chances of its propagation from live to dead-end hence, improving the breakdown strength. The physical and chemical nature of nanofillers has a crucial impact on increasing the resistance to treeing. In this paper, phase-field model is developed and used to simulate electrical treeing in polyethylene for varying concentrations of alumina nanofiller using COMSOL Multiphysics. Tree inception time, tree-growth patterns, and corresponding changes in dielectric strength is studied for both dispersions. Electrical treeing under different concentrations of alumina nanofillers with uniform and nonuniform dispersion is investigated in polyethylene as a base material. It is observed that fillers with uniform dispersion increases the resistance to treeing and tree inception time. Highest resistance to treeing is observed by adding 1% nanoalumina uniformly in raw polyethylene. Moreover, in uniform dispersion the tree deflects into multiple branches earlier than nonuniform dispersion impeding the damage speed as well.A phase-field model is developed in this paper based on the similarity between mechanical fracture and dielectric breakdown. Electrical treeing is associated with the dielectric breakdown in solid dielectrics by the application of high voltages. Instead of explicitly tracing the propagation of conductive channel, this model initializes a continuous phase field to characterize the extent of damage. So far, limited research has been conducted for simulating the effect of nanofiller dispersion on electrical treeing. No study has modeled the effect of uniform and nonuniform dispersion of nanofillers with varying filler concentration on treeing. Since electrical treeing tends to decrease the breakdown strength of solid dielectrics therefore, nanofillers are widely used to distract the tree from a straight channel to distribute its energy in multiple paths. Diverting a straight treeing channel into multiple paths reduces the chances of its propagation from live to dead-end hence, improving the breakdown strength. The physical and chemical nature of nanofillers has a crucial impact on increasing the resistance to treeing. In this paper, phase-field model is developed and used to simulate electrical treeing in polyethylene for varying concentrations of alumina nanofiller using COMSOL Multiphysics. Tree inception time, tree-growth patterns, and corresponding changes in dielectric strength is studied for both dispersions. Electrical treeing under different concentrations of alumina nanofillers with uniform and nonuniform dispersion is investigated in polyethylene as a base material. It is observed that fillers with uniform dispersion increases the resistance to treeing and tree inception time. Highest resistance to treeing is observed by adding 1% nanoalumina uniformly in raw polyethylene. Moreover, in uniform dispersion the tree deflects into multiple branches earlier than nonuniform dispersion impeding the damage speed as well.

由于氮化铝纳米线具有优异的导热性, 国内外学者对其进行了广泛研究。本文以三聚氰胺和氟化钇为添加剂, 采用直接氮化法制备了氮化铝纳米线。利用X射线衍射(XRD)、扫描电镜(SEM)、高分辨率透射电子显微镜(HRTEM)、能谱仪(EDS)等表征了氮化铝纳米线的晶体结构和微观形貌, 分析了三聚氰胺和氟化钇对氮化反应的促进作用, 研究了不同含量的三聚氰胺和不同反应温度对制备氮化铝纳米线的影响。结果表明: 添加三聚氰胺可以提高氮化反应速率, 促进纳米线的生成; 当反应温度为1 200 ℃, 铝粉和三聚氰胺质量比为1∶4, 氟化钇掺量为5%(质量分数)时, 成功制得了高长径比的氮化铝纳米线。

为了明晰光丝距离对激光填丝焊接过程影响规律, 采用高速摄像、外观检查、宏观金相等方法, 对3种光束模式下不同光丝距离与激光堆焊关系进行了理论分析和实验验证, 得到了光丝距离对焊丝熔化、熔滴过渡、熔池波动和焊缝凝固的稳定性影响数据。结果表明, 光丝位置由相交(-5mm)向相离(+5mm)变化时, 熔滴过渡经历“液滴→液滴+液桥→液桥→液滴+液桥”阶段; 相同光丝距离时, 单光束激光模式、双光束激光串行模式和双光束并行模式的焊缝熔深依次降低, 甚至出现焊缝偏移和无熔深现象; 单光束模式和双光束串行模式对焊丝熔化和熔池的影响规律近似, 但双光束并行模式下具有特殊性; 单光束激光焊接时, 随着离焦量的增加, 焊缝的熔深由最大值409.8μm迅速减小到282.6μm; 双光束激光串行模式时, 焊缝的最大熔深仅为328.4μm, 随着离焦量降低而减小, 但正离焦量为焊缝截面呈现不对称状态; 双光束激光并行焊接模式时, 焊丝偏向小功率激光束时, 焊缝无熔深; 随着焊丝向大功率激光束移动, 形成仅有226.5μm小熔深焊缝。该研究为铝合金激光增材和焊接提供了参考。

激光填粉焊接技术可实现大裕度、高质量的柔性焊接,相较于传统焊接技术具有不可比拟的优势。基于GH3030高温合金开展相关工艺试验,研究了不同的激光功率、扫描速度、离焦量对焊接表面形貌、抗拉强度的影响,并分析了不同离焦量下的金相组织。在激光功率2 100 W、扫描速度900 mm/min、离焦量为+2 mm时,可以获得一定熔宽且均匀连续、无缺陷的焊缝；在较优的工艺参数下,焊接后抗拉强度优于母材。各工艺参数的选取对焊接接头的抗拉强度影响很大,在实现良好冶金结合的前提下,避免晶粒粗大、组织疏松是提升抗拉强度的关键。