扫描间距对45钢激光熔凝强化组织性能的影响

为了研究扫描间距对45钢激光熔凝强化组织性能的影响,采用HLD1001-5 型固体激光器对45钢表面进行了多条带等间距激光熔凝处理,分别利用扫描电镜、洛氏硬度计、磨损试验机观察和测量了不同扫描间距下硬化层的显微组织及性能。结果表明：激光熔凝处理的硬化层由熔化区、相变硬化区和热影响区组成,组织为马氏体;多条带等间距激光熔凝处理在垂直于熔凝条带方向上的硬度分布由左高硬度区、左过渡区、低硬度区、右过渡区和右高硬度区组成,高硬度区的硬度为58.1～59.6 HRC,低硬度区的硬度约16 HRC;在试验范围内,经激光扫描间距为4.5 mm 熔凝处理的试样具有最好的耐磨性。     

Summer Dormancy in Phalaris aquatica L., the Influence of Season of Sowing and Summer Moisture Regime on Two Contrasting Cultivars

A series of trials to increase understanding of the summer dormancy trait in Phalaris aquatica was conducted. Autumn‐sown and younger, spring‐sown plants of two cultivars (cvv), known to contrast in expression of summer dormancy, were established and then tested over the following summer under three moisture regimes: long drought; drought + mid‐summer storm; or full irrigation. The autumn‐sown plants of cv. Atlas PG expressed substantial but incomplete summer dormancy under all moisture regimes and exhibited the characteristic responses including significant growth reduction and herbage senescence. The summer‐dormant cv. Atlas PG used 31 mm less soil water over the summer and also began to rehydrate its leaf bases from conserved soil water before the drought broke. The non‐dormant cv. Australian grew whenever moisture was applied and also responded to the mid‐summer storm with a decline in dehydrin expression in leaf bases, whereas no decline occurred in Atlas PG, presumably because it remained dormant. The irrigated, younger, spring‐sown swards of cv. Atlas PG had restrained growth and produced only about 37 % of the herbage of cv. Australian. Drought reduced activity and growth of young plants of both cultivars but while Australian regrew in response to the storm, cv. Atlas PG, grew much less (59 % of Australian) indicating that dormancy, although only partially expressed after spring sowing, was reinforced by summer drought. Australian used more soil water over summer than Atlas PG, and it is suggested that this is why cv Australian is limited to the higher rainfall zones of south‐eastern Australia, particularly where soil water holding capacity is limited.