Microstructure and mechanical properties of hot extruded Mg–Al–Mn–Ca alloy produced by rapid solidification powder metallurgy

The microstructure and mechanical properties of hot extruded Mg–Al–Mn–Ca alloy was investigated. Both rapid solidified powders and cast billets were extruded at 573, 623 and 673 K to optimize the processing conditions for obtaining better mechanical response. Powder was consolidated to prepare the extrusion billets using both cold compaction and Spark Plasma Sintering at 473 K. The tensile properties of the extruded alloy were then evaluated and correlated to the observed microstructure. The results show that the use of rapid solidified powder could lead to effective grain refinement, which in turn resulted in the improved mechanical response, especially compared to the extruded conventional cast material.     

Cyclic cracking resistance of brittle materials under compressive loading

Fatigue behavior of brittle materials under compression is considered. The findings should be taken into account in the failure probability assessment of components made of materials with limited plasticity, which are used in various stress states. __________ Translated from Problemy Prochnosti, No. 1, pp. 83–87, January–February, 2009.     

1Cr18Ni9Ti不锈钢输油管道开裂原因分析

通过化学成分分析、宏观检验、金相检验和断口分析等方法对1Cr18Ni9Ti不锈钢液压油输送管道开裂原因进行了分析。结果表明:不锈钢管开裂为应力腐蚀开裂,裂纹起源于管道外壁并逐渐向内壁扩展;产生开裂的主要原因是工业水中氯、硫和氧等腐蚀性物质不断在钢管外壁沉积,在管道压力和腐蚀介质共同作用下,不锈钢管发生应力腐蚀开裂。     

Experimental Investigation of Bond Stress and Deformations in LWAC Ties Reinforced with GFRP Bars

The structures' durability is an engineering concern for a long time but has been increased in the last years. Lightweight aggregate concrete (LWAC) combined with glass fibre reinforced polymer bars allows to create structures with high performance in terms of durability. The glass fibre reinforced polymer (GFRP) bars have different ribs from those of steel bars, and consequently, its bond to concrete is affected. Moreover, the Young's modulus of GFRP is much below compared with that of steel, and this influences significantly the behaviour of structural elements reinforced with this material. This paper presents an experimental study focused on bond between LWAC and reinforcing bars of GFRP. Thirty‐six pull‐out tests were carried out using steel and GFRP bars. These reinforcements were combined with three types of concrete, all with the same design density 1900 kg m^?3 but with different values of compressive strength: 35, 55 and 70 MPa. Furthermore, 12 reinforced ties were tested, combining different types of bars (steel and GFRP), two different diameters (12 and 16 mm) and the three types of LWAC. Based on experimental results, several relations were established to understand the behaviour of LWAC structures reinforced with GFRP bars, mainly in the serviceability conditions. These results point out that ties deformation and crack width are very affected by the reduced Young's modulus of GFRP: deformations and crack width of ties reinforced with GFRP are significantly higher, approximately three times greater, compared with those of ties reinforced with steel. The tension stiffening effect was also analysed in detail, and it was found that it is slightly influenced by the concrete compressive strength but is highly dependent of the Young's modulus of the reinforcing material.     

Microstructure and Its Influence on Mechanical Behaviour of Directionally Solidified DZ38G Superalloy

The features of microstructure and theirinfluence on mechanical properties onstress-rupture as well as thermal fatigue ofdirectionally solidified DZ38G nickel-base su-peralloy have been investigated.It has beenfound that the contents of carbides on grainboundaries are increased and morphology of γ'-precipitates has been changed after testing.Particularly γ'-precipitates coalesced intoraft-like in morphology perpendicular to theapplied stress-axis have been observed thathas no detrimental effect on the stress-rupturebehaviour.The tendency of σ-formation hasalso been discussed.The σ-phase can be avoidedwhen the process parameters are chosenappropriately during solidification.     

镍基单晶高温合金研究进展

单晶高温合金因具有较高的高温强度、优异的蠕变与疲劳抗力以及良好的抗氧化性、抗热腐蚀性、组织稳定性和使用可靠性,广泛应用于涡轮发动机等先进动力推进系统涡轮叶片等部件。由于采用定向凝固工艺消除了晶界,单晶高温合金明显减少了降低熔点的晶界强化元素,提高了合金的初熔温度,能够在较高温度范围进行固溶和时效处理,其高温强度比等轴晶和定向柱晶高温合金也大幅度提高。经过几十年的发展,单晶高温合金已经在合金设计方法、组织结构与力学性能关系、纯净化冶炼工艺和定向凝固工艺等方面取得了重要进展。从单晶高温合金成分特点、合金元素作用、强化机理、力学性能各向异性、凝固过程及缺陷控制、单晶制备工艺等方面,简要介绍了单晶高温合金的主要研究进展。     

左右后门框下部外板冲压工艺改进

通过解析一个汽车零件的冲压工艺设计及CAE分析模拟方案的可行性,重点记录了此零件拉深时由于拉深难度大导致的破裂以及降低拉深深度时出现的翻边缺料破裂的解决过程,从而避免了大批模具报废的严重后果。     

锅炉水冷壁管横向裂纹故障机理分析

根据国产 Ｈ Ｇ２００８ 控制循环锅炉和 Ｓ Ｇ１０００ 直流锅炉水冷壁壁温测定结果和炉管受力分析,探讨了锅炉水冷壁管横向裂纹性及造成炉管破的的机理,并分析了产生横向裂纹故障的主要原因。     

管线用钢显微组织对氢致裂纹影响的研究

选用了四种不同显微组织的国产同牌号管线用钢,根据美国腐蚀工程师协会标准NACETM0284-2003,对其进行氢致开裂实验,并用光学显微镜和扫描电镜对其断面组织进行了观察,分析其显微组织对抗氢致裂纹性能的影响。认为,带状组织以及组织不均匀性是引起材料抗氢致裂纹性能下降的主要因素,但这两种因素引起开裂的方式和机理不同。同时发现晶粒度大小对该材料抗氢致裂纹性能没有明显影响。     

脉冲电流在改善金属凝固组织中的作用

综述了脉冲电流在改善金属凝固组织方面的研究现状。从理论上归纳和分析了脉冲电流在金属凝固过程中产生作用的主要机制。