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首页> 外文期刊>Materials transactions >Thermoelastic equilibrium and specimen size effects in thermoelastic martensitic transformations
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Thermoelastic equilibrium and specimen size effects in thermoelastic martensitic transformations

机译：热弹性马氏体相变中的热弹性平衡和试样尺寸效应

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New thermodynamical concepts are introduced in thermoelastic martensitic transformations, since the conventional thermodynamical scheme cannot explain the upward shifts in M{sub}x and in experimentally determined equilibrium temperatureT{sub}o{sup}☆=(M{sub}s+A{sub}f)/2 with increasing specimen size which have been experimentally observed in Ti-Ni and Cu-Al-Ni alloys. The first concept is that the total free energy of phases G{sub}tot which is the sum of chemical free energyG{sub}(chem) and nonchemical free energy G{sub}(nonc) (such as elastic strain energy E{sub}(elas), which is generated through the shape change attending martensitic transformations, and interfacial energy E{sub}(face)), equals at T{sub}o{sup}☆.Increasing specimen size increases E{sub}(elas) more in parent than in martensite. The larger E{sub}(elas) in the parent phase than in the martensite destabilize parent phase, resulting in the upward shift in T{sub}o{sup}☆. The second concept is thetotal free energy of a system, G{sup}#=fG{sub}tot{sup}M+ (1-f)G{sub}tot{sup}p where the symbol f indicates the transformation fraction, the superscript M martensite, and P is the parent phase. On the basis of the concept, thermoelastic equilibrium inthermoelastic martensitic transformations is formulated as -f△G{sub}chem{sup}(P→M)(T)=fG{sub}nonc{sup}M(f)+(l-f)G{sub}nonc{sup}p(f). Further, the evolution of G{sup}# on cooling is found to be expressed as G{sub}chem{sup}p(T) even below M{sub}s up toM{sub}f under the thermoelastic equilibrium. The third is that the supercooling below T{sub}o{sup}☆ to M{sub}s for the onset of the transfomations is not because necessary G{sub}nonc has to be provided through chemical driving force but because of thepresence of a potential energy barrier against pseudoshear movement of the atom cluster in the parent phase to martensite. The concept enables us to elucidate the experimentally observed upward shift of M{sub}s with increasing specimen size.
机译：由于传统的热力学方案无法解释M {sub} x和实验确定的平衡温度T {sub} o {sup}☆=（M {sub} s + A { }}}）随着样品尺寸的增加而增加，这在Ti-Ni和Cu-Al-Ni合金中已通过实验观察到。第一个概念是相G {sub} tot的总自由能，即化学自由能G {sub}（chem）和非化学自由能G {sub}（nonc）之和（例如弹性应变能E {sub }（elas）是通过伴随马氏体相变而发生的形状变化和界面能E {sub}（face））产生的，等于T {sub} o {sup}☆。增加试样尺寸会增加E {sub}（elas ）在母体中比在马氏体中更多。母相中的E {sub}（elas）比马氏体破坏母相中的大，导致T {sub} o {sup}☆向上移动。第二个概念是系统的总自由能G {sup}＃= fG {sub} tot {sup} M +（1-f）G {sub} tot {sup} p，其中符号f表示变换分数，即上标M为马氏体，P为母相。根据该概念，将热弹性平衡热弹性马氏体转变公式表示为-f△G {sub} chem {sup}（P→M）（T）= fG {sub} nonc {sup} M（f）+（lf ）G {sub} nonc {sup} p（f）。此外，发现在热弹性平衡下，甚至在M {sub} s以下直至M {sub} f以下，冷却时的G {sup}＃的演变被表示为G {sub} chem {sup} p（T）。第三点是，在转变开始时，T {sub} o {sup}☆到M {sub} s以下的过冷不是因为必须通过化学驱动力提供必要的G {sub} nonc，而是因为存在潜在的能垒，阻止原子团簇在母相中向马氏体的假剪切运动。该概念使我们能够阐明实验观察到的M {sub} s随样品尺寸的增加而向上移动的情况。

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