Nanostructured Materials
Nanocrystalline (NC) Ni-P alloy samples with average grain sizes ranging from a Sew to 127 nm have been produced by crystallizing the amorphous Ni-P alloy at various annealing temperatures. The linear thermal expansion coefficients (alpha(I)) of these NC samples were accurately measured in a temperature range of 300-400K. Experimental results showed that alpha(L) is heavily dependent on the grain size and decreases from about 20.7x10(-6) to 15.5x10(-6) K-1 with an increase in the average grain size from 7.5 to 127 nm. From the alpha(L) dependence of grain size in these NC samples and the at value of the as-cast coarse-grained polycrystalline Ni-P sample we deduced that the difference in thermal expansion coefficients of the interfaces and ofthe nm-crystallites decreases with a reduction of grain size.
关键词:
ultrafine grains
蓝慧芳
,
W.J.Liu
,
刘相华
材料研究学报
在低碳钢和低碳加铌、钒、钛微合金钢中,通过马氏体冷轧--回火的方法获得了尺寸为数百纳米的超细晶粒铁素体组织,研究了超细晶粒组的形成机制和热稳定性. 通过马氏体相变在这些钢中引入了大量高密度位错,马氏体冷轧后位错进一步增殖, 形成大量位错胞状结构;在500-600℃进行的60 min回火将上述胞状结构转变成具有清晰大角晶界的超细晶粒.在回火过程中形成的微合金元素碳化物对位错运动和晶界移动具有有效的“钉扎”作用,有助于获得超细晶组织并明显提高其热稳定性.
关键词:
金属材料
,
cold rolled martensite
,
tempering
,
microalloyed steel
,
precipitation
王晨曦
,
石磊
,
徐杰
,
单德彬
,
郭斌
材料科学与工艺
doi:10.11951/j.issn.1005-0299.20160101
为了研究超细晶纯铝热变形行为,利用等通道挤压工艺制备了超细晶纯铝,并采用INSTRON 5965材料电子万能试验机对超细晶纯铝进行了高温微压缩实验,分析了超细晶纯铝在150~250 ℃、应变速率3.3 ×10-4~1 ×10-1 s-1条件下流动应力的变化规律.研究表明,流动应力随试样尺寸的减小呈下降趋势,且变形温度和应变速率对流动应力有显著影响,流动应力随变形温度的升高和应变速率的降低而降低.基于双曲正弦形式修正的Arrhenius关系的本构模型,建立了超细晶纯铝高温微压缩变形本构关系.实验验证表明,所建立的本构关系能够较好地反映超细晶纯铝高温微塑性变形行为特征.
关键词:
纯铝
,
超细晶
,
微成形
,
热变形
,
本构关系
