Dislocation±disclination model of heterogeneous nucleation of HCP-martensite M.Yu. Gutkin * ,1 , K.N. Mikaelyan 1 , and V.E. Verijenko School of Mechanical Engineering, University of Natal, Durban 4041, South Africa Received 12 February 2001; accepted 7 July 2001 Abstract Adislocation±disclinationmodelisproposeddescribingheterogeneousnucleationofanembryoofhcp- martensite at a tilt grain boundary segment containing some extrinsic dislocations. The corresponding energy gain is analysed in detail. The equilibrium and critical embryo sizes under external conditions of temperatureandstressareexaminedanddiscussed. Ó 2001PublishedbyElsevierScienceLtd.onbehalfof Acta Materialia Inc. Keywords: Heterogenous phase transformation; Martensite nucleation; Theory of defects; Grain boundaries; Disloca- tions Introduction Martensiticfcc ! hcpphasetransformationhasextensivelybeeninvestigatedduring thelast70years.Themechanismsandconditionsofitsrealisationhavebeenstudiedby many authors on various materials such as Fe-based alloys and steels. Fe±Mn [1±9], Fe±Mn±Co[3,7],Fe±Mn±Cr[3],Fe±Mn±Mo[10],Fe±Mn±Ni[3],Fe±Mn±Si[6,11±14], Fe±Mn±Si±Cr±Ni [15,16], Fe±Cr±C [17], Fe±Cr±Ni [2,3,18±21]; pure Co [22±24] and Co-based alloys Co±Cr±Mo [25±27], Co±Fe [28], and Co±Ni [29,30]. In recent years, specialattentionhasbeenpaidtothismartensitictransformationMT)foritskeyrole in shape memory [11±16], damping [5] and orthopaedic implant alloys [25±27]. On the otherhand,thefcc ! hcpMTrepresentsthesimplestcaseamongotherMTsandmay be considered as a good model example for better understanding the nature and propertiesofMTs.However,thenumberofappropriatetheoreticalmodelslooksquite limited. Christian [22] suggested that the fcc ! hcp MT can be accomplished by the Scripta Materialia 45 2001) 939±945 www.elsevier.com/locate/scriptamat * Corresponding author. Fax: +7-812-321-4771. E-mail address: gutkin@def.ipme.ru M.Yu. Gutkin). 1 On leave from: Institute of Problems of Mechanical Engineering, Russian Academy of Sciences, Bol'shoj 61, Vasilievskij Ostrov, St. Petersburg 199178, Russia. 1359-6462/01/$-seefrontmatter Ó 2001PublishedbyElsevierScienceLtd.onbehalfofActaMaterialiaInc. PII:S1359-646201)01115-0