用低压渗流法制备泡沫铝合金

用低压渗流法生产泡沫铝合金，研究了影响液体金属渗流高度的工艺参数，实验表明，渗流高度随着颗粒的预热温度，外加渗流压力和铝液浇注温度的升高而增加，其中颗粒预热温度的影响最为显著，其他因素的影响不大，实验还表明，颗粒尺寸对于降低渗流高度起了重要作用，颗粒尺寸越小，渗流高度越低，对于不同尺寸的颗粒，都存在一个临界预热温度。     

颗粒流中的冲击力

作者通过实验研究了宽沟道内颗粒流冲击力沿沟道的分布,不同半径圆形颗粒的冲击力,还研究了冲击力谱曲线的渡越行为。实验结果表明：颗粒流稳定时,冲击力在沟道横向呈抛物线形分布;冲击力随着滑移距离L增大衰减;对于单一尺寸颗粒流,稳定时冲击力随着颗粒直径增大而增大;对于不同尺寸的混合颗粒流,冲击力随不同尺寸颗粒质量比增大先增加最后趋于饱和,存在指数关系;结果还表明力谱曲线的上升沿和下降沿有明显区别。结果对实验研究不同固相比泥石流冲击特性或泥石流理论研究提供科学借鉴。     

地下水渗流对垂直埋管换热器换热性能影响的实验研究

地埋管换热器的换热性能是地源热泵空调系统设计的关键问题之一。建立了地源热泵砂箱实验台,实验研究了地下水渗流对地源热泵地埋管换热器换热性能的影响。研究结果表明:地下水渗流可以强化地埋管的换热,且随着渗流速度的增大,强化换热作用越明显。另外,实验结果也表明,U型管周围温度峰值的位置会沿渗流方向向下游偏移,地埋管群布置时应避开该位置,以强化埋管的换热。     

泡沫铝合金渗流铸造工艺的试验分析EI

采用正交实验方法 ,选择三种不同粒径的填料 ,系统研究了粒子预热温度、金属液浇注温度和充型压力对渗流铸造泡沫铝合金成型工艺的影响 ,并对试验结果作了理论分析。认为 ,合理选择粒子预热温度是生产泡沫金属铸件的前提 ,适当提高浇注温度是保证泡沫组织均匀良好的关键 ,保持适度的充型压力有利于提高材质通孔率和工艺稳定性。     

不同焊接条件下TIG焊接紫铜厚板的热效应研究

为改善紫铜厚板的焊接性,采用商业有限元软件Marc对钨极气体保护焊接紫铜厚板的温度场进行模拟,并详细讨论了焊接电流以及预热温度对熔池和热影响区的影响.结果表明,熔池和热影响区均随着预热温度和焊接电流的增加而增加,因此,在采用不同的预热温度和焊接电流的组合可以得到相同尺寸的熔池,但热影响区尺寸差别很大;在20℃时采用He或N2气保护焊得到的熔池尺寸与Ar气保护预热400℃时得到的熔池尺寸基本一致,但热影响区的尺寸窄于Ar气保护预热400℃时得到的热影响区尺寸.     

泡沫铝合金制备工艺研究

采用正交实验方法，选择三种不同粒径的填料，系统研究了粒子预热温度、金属液浇注温度和充型压力对渗流铸造泡沫铝合金成型工艺的影响，并对试验结果作了理论分析。认为，合理选择粒子预热温度是生产泡沫金属铸件的前提，适当提高浇注温度是保证泡沫组织均匀良好的关键，保持适度的充型压力有利于提高材质通孔率和工艺的稳定性。     

SiC颗粒尺寸对喷射共沉积7075 Al/SiCp挤压及轧制的组织和性能的影响

研究了喷射共沉积方法制备的7075 Al / SiCp复合材料挤压及轧制过程中SiC颗粒的分布.通过拉伸实验、微观组织的金相及拉伸断口SEM观察分析了SiCp颗粒尺寸对材料组织和性能的影响.实验表明,SiCp在挤压过程中沿厚度方向形成分层分布,SiCp的尺寸及粒度分布对于聚集有较大的影响;轧制过程对挤压时形成的SiCp分层分布有一定的减弱作用,但改善程度和SiCp的尺寸有关;SiCp颗粒尺寸对复合材料的力学性能及断裂机制有很大的影响.     

不锈钢基体温度对NiCrCoAlY 和ZrO2涂层颗粒变形的影响

研究了等离子喷涂过程中, 不同基体预热温度下NiCrCoAl Y金属与ZrO₂ 陶瓷颗粒的变形规律。结果表明: 基体无预热时, NiCrCoAl Y金属颗粒沉积形貌呈盘形, 并伴随边缘堆积和飞溅碎块等不规则现象, 影响后续颗粒的顺利铺展; 基体预热至200 ℃时, 不规则现象减少, 后续颗粒铺展良好。ZrO₂ 颗粒在基体无预热条件下凝固后呈圆盘状, 并产生龟裂纹和条束状溅射, 随着基体预热温度的升高, 龟裂和溅射现象减少。基体预热对NiCrCoAl Y涂层孔隙率影响不大, 而ZrO₂涂层在基体预热至200 ℃时孔隙率明显降低。      

VPI法制备温度对Al2O3/水泥基材料组织和力学性能的影响北大核心CSCD

以Al2O3颗粒来实现对水泥基材料的增强效果,通过真空压力浸渗法制得具有连续结构的Al2O3/Ce基材料,分析预热温度对材料显微组织及力学性能的影响。研究结果表明:随着处理温度的升高,Al2O3/Ce基材料达到了更大的致密度。随着预热温度的增加,试样孔洞数量减少,孔隙率减低。当预热温度600℃时,Al2O3/Ce基组织内形成了具有均匀粒径的颗粒,获得最优的浸渗效果。Al2O3颗粒具有良好耐热性以及耐蚀性能,经拉伸测试发现当预热温度上升后颗粒拉伸强度发生了减小。随着预热温度的增加,试样断口部位颗粒拔出长度减少,颗粒与界面间的结合能力增加。经过600℃预热试样形成了整齐的拉伸断口,裂纹在颗粒径向上发生了快速扩展,对承载面形成了贯穿,发生脆性断裂。     

VPI法制备温度对Al_2O_3/水泥基材料组织和力学性能的影响

以Al_2O_3颗粒来实现对水泥基材料的增强效果,通过真空压力浸渗法制得具有连续结构的Al_2O_3/Ce基材料,分析预热温度对材料显微组织及力学性能的影响。研究结果表明:随着处理温度的升高,Al_2O_3/Ce基材料达到了更大的致密度。随着预热温度的增加,试样孔洞数量减少,孔隙率减低。当预热温度600℃时,Al_2O_3/Ce基组织内形成了具有均匀粒径的颗粒,获得最优的浸渗效果。Al_2O_3颗粒具有良好耐热性以及耐蚀性能,经拉伸测试发现当预热温度上升后颗粒拉伸强度发生了减小。随着预热温度的增加,试样断口部位颗粒拔出长度减少,颗粒与界面间的结合能力增加。经过600℃预热试样形成了整齐的拉伸断口,裂纹在颗粒径向上发生了快速扩展,对承载面形成了贯穿,发生脆性断裂。     

Synthesis of Porous Composite Materials via Combustion of a Mixture of Titanium,VT6 Alloy,and Amorphous Boron Powders

Self-propagating high-temperature synthesis without preheating has been realized in powder mixtures consisting of large spherical VT6 titanium alloy granules, small dendritic titanium particles, and black amorphous boron. Synthesis in a combustion wave involved a few steps: first, boron reacted with fine-particle titanium to form a boride matrix, which then reacted with molten VT6 titanium alloy granules. We have obtained a porous metal–ceramic material similar in structure to composites.     

Effects of melt temperature and mold preheating temperature on the fluidity of Ca containing AZ31 alloys

The effects of melt temperature and mold preheating temperature on the fluidity of Ca containing AZ31 alloys were evaluated under various casting conditions. The flow lengths of AZ31-xCa alloy melt increased with increasing the melt temperature due to lower viscosity and longer time to fill the mold cavity. The increment of the flow lengths of AZ31-xCa alloy melt with increasing the mold preheating temperature was not large due to large diameter of circular cross section of mold cavity. The fluidity of AZ31-xCa alloy melts was affected more forcefully by melt temperature than by mold preheating temperature under casting conditions used in this study. Also, the flow lengths of AZ31-xCa alloy melt were affected by grain size of primary solid particles solidified during filling mold cavity and surface oxide film due to addition of Ca.     

激光多层熔覆纳米陶瓷层工艺参数优化

为了深入了解激光多层熔覆工艺与涂层性能之间的关系,采用压片预置式激光多层熔覆工艺制备了纳米Al2O3-13%TiO2(质量分数)陶瓷层;通过3因素3水平正交试验分析了激光熔覆熔池闭环控制温度、超声振动频率及保温箱预热温度对涂层结合强度的影响,并对激光熔覆工艺参数进行了优化;通过扫描电镜(SEM)和结合强度测试研究了最优工艺下所得涂层的形貌和性能。结果表明:影响涂层结合强度的因素主次顺序依次为熔池闭环控制温度、保温箱预热温度、超声振动频率;激光多层熔覆纳米Al2O3-13%TiO2涂层最佳工艺参数为熔池闭环控制温度2 500℃,超声振动频率50 kHz,保温箱预热温度400℃;优化工艺熔覆的涂层各层之间无明显界面,涂层内部致密、连续,基本无孔隙及贯穿性大裂纹,涂层结合强度明显提高,达66.3 MPa。     

预热温度对铝镁合金厚板焊接接头组织与力学性能的影响

研究了不同预热温度下5383铝镁合金50 mm厚板焊接接头的力学性能、断口形貌及金相组织。试验结果表明,采用较低的预热温度,虽能实现焊缝的良好成型,内部质量优,但其力学性能偏低。较低的预热温度会导致熔池温度偏低,使母材中大量存在的富FeMn相不能完全熔化而出现偏聚,从而导致焊缝局部塑性和强度变差。      

Casting of TiC-Reinforced Steel Matrix Composite

Titanium carbide varying from 6.34 to 21.60 volume fraction was reinforced in to iron matrix by the direct reaction of pure titanium in molten Fe-C alloy. A simple casting technique has been developed successfully to improve the precipitation and distribution of titanium carbide particles in iron matrix. Lime powder is used as a protective layer on the molten metal to avoid oxidation of titanium during melting and casting. The thermodynamic and kinetic studies support the precipitation of TiC in molten Fe-C alloy at the reaction temperature, 1600°C. The size and shape of the in-situ TiC particles depend on the amount of titanium present in Fe-C molten alloy.     

Measurement and Analyses of Molten Ni-Co-A1 Alloy Density

The density of molten Ni-Co-Al alloy was measured using a modified pycnometric method. It has been found that the density of the molten Ni-Co-Al alloy decreases with increasing temperature, Co concentration and the ratio of Co concentration to Ni concentration in the alloy. The coefficient of volume expansion of the molten Ni-Co-Al alloy decreases with increasing Co concentration and the ratio of Co concentration to Ni concentration. The temperature coefficient of density increases with increasing the Co concentration or the ratio of Co concentration to Ni concentration in the alloy. The density of the molten Ni-Co-Al alloy as functions of both temperature and Co concentration was expressed.     

Measurement and Analyses of Molten Ni-CO-Al Alloy Density

The density of molten Ni-Cd-Al alloy was measured using a modified pycnometric method.It has been found thatthe density of the molten Ni-Co-Al alloy decreases with increasing temperature Co Concentration and the ratioof Co concentration to Ni concentration in the alloy.The coefficient of volume expansion of the molten Ni-Co-Al alloy decreases with increasing Co concentration and the ratio of Co concentration to Ni concentration.Thetemperature coefficient of density increases with increasing the Co concentration or the ratio of Co concentration toNi concentration in the alloy.The density of the molten Ni-Co-Al alloy as functions of both temperature and Coconcentration was expressed.     

Effect of substrate preset temperature on crystal growth and microstructure formation in laser powder deposition of single-crystal superalloy

A successful repair of single-crystal components needs to avoid the stray grain formation and achieves continuous epitaxial growth of columnar dendrites in the repaired zone. In this study, the effect of substrate preset temperature on crystal growth and microstructure formation in laser powder deposition of single-crystal superalloy was studied through an improved mathematical model and corresponding experimental approaches. The results indicated that the variation of substrate preset temperature between ?30?°C and +210?°C changes the molten pool morphology little, but obviously affects the columnar-to-equiaxed transition conditions. The preheating of substrate facilitates the stray grain formation and enlarges the primary columnar dendrite arm spacing, while the situation for precooling of substrate is opposite. Under the specific processing conditions, the critical condition for continuous epitaxial growth is that the substrate preset temperature T_sub?≤?+90?°C. When the substrate preset temperature T_sub is below +90?°C, the height ratio of melting depth to total height of the molten pool is larger than that of stray grain, ensuring that stray grains can be completely remelted and the continuous columnar dendrites during the multi-layer laser powder deposition process on (001) surface of single-crystal substrate can be achieved.     

Effect of heat-input and cooling-time on bead characteristics in SAW

Load-carrying capacity of weld joints could be identified by its shape and size where weld bead geometry and shape relationship parameters are of utmost importance. Heat input and preheating temperature together can control the cooling time of weld, which in turn determines the weld microstructure and its mechanical properties. To control the shape and geometry of weld bead, it is necessary to understand its relationship with cooling time. In present work, preheating temperature is used as process variable along with heat input varying parameters for understanding their effects on weld bead geometry and shape relationship parameters using submerged arc welding process on high-strength low alloy pipeline steel. The experimental investigation was then analyzed by using the mathematical modeling in context with response surface methodology. The mathematical model predicts the influential dependency of cooling time on the preheating temperature than the other weld process parameters. The associated effects in relation to the process parameters have been discussed and analyzed in the present study.