烘-浸交替提高混凝土性能的试验研究

针对合理的养护以提高中等强度混凝土性能的问题,以普通混凝土试件和掺入低质灰作为辅助性胶凝材料的粉煤灰混凝土试件为研究对象,室温养护28d和90d后进行烘-浸及少量冻-融试验并测量两类试件的抗压强度和弹性模量。结果表明:28 d龄期至90 d龄期间,经适宜的烘-浸交替作用,普通混凝土和粉煤灰混凝土均达到了比设计强度高一个强度等级的效果。说明高温洒水养护不仅对早期强度有利,对一定时间内混凝土强度的提升仍有很好的作用。该结果对实际工程中重视28d-90d龄期之间混凝土的养护具有一定的指导意义。     

Influence of hot-rolling on the microstructure and mechanical properties of a near β-type Ti-5.2Mo-4.8Al-2.5Zr-1.7Cr alloy

In this work, the 90° clock rolling and the uni-directionally rolling processes at high temperature were carried out on the near β-type Ti-5.2Mo-4.8Al-2.5Zr-1.7Cr titanium alloy cutting from an ingot, respectively. The corresponding microstructures were quantitatively characterized, and its effect on the dynamic mechanical properties and fracture mechanism were emphatically investigated. It was found that after 90° clock rolling, the microstructure composed of equiaxed primary α phase(α_p) with an average size of about 2 ?μm and the β transformed regions containing the acicular secondary α phase(α_s) with an average thickness of about 50 ?nm and the separated β phase was obtained. However, in the uni-directionally rolled titanium alloy, no acicular α_s was observed, and the corresponding microstructure consisted elongated lamellar α phase (average thickness: about 1.3 ?μm), few equiaxed α phase (average grain size: about 300 ?nm) and the inlaid β phase. The microstructural difference of the hot-rolled titanium alloys was closely related to the deformation process. Moreover, a great number of α_p and α_s in the 90° clock rolled titanium alloy effectively enhanced the strength, and the dynamic compressive strength reached to 1730 ?MPa. Furthermore, equiaxed α_p was conducive to the homogeneous deformation, which counteracted the localized deformation caused by acicular α_s to a certain extent and made the 90° clock rolled titanium alloy exhibit an acceptable critical fracture strain of about 10.5%. Moreover, the fracture microstructures showed that the main failure mode of the 90° clock rolled and the uni-directionally rolled titanium alloy were ductile fracture and brittle fracture, respectively.     

5A90铝锂合金显微组织及力学性能的研究

利用光学显微镜、扫描电镜及高分辨透射电镜等手段研究了5A90铝锂合金轧板经热处理后的显微组织与力学性能.结果表明:5A90合金轧板组织呈明显的各向异性,合金板材轧制平面的晶粒呈等轴状,纵截面和横截面均为轧制流线组织,有少量细小的再结晶晶粒；合金经460℃/20 min固溶处理后,在130℃时效过程中,随着时效时间的延长...