Some Factors Affecting on the Structure-formation and Mechanical Properties of As-Cast High Toughness Nodular Cast Iron

D0I:10.13374/j.issn1001-053x.1989.06.029 第11卷第6期 北京科技大学学报 Vol.11 No.6 1989年11月 Journal of University of Science and Technology Beijing Nov,1989 Interfacial Phase in Ti-5Al-2Mo-3Zr Alloy' Deng Yongrui(邓永瑞)Qiu Dongyao(邱东)， Qin Zehua(秦泽华)，· ABSTRACT:Under appropriate cooling condition,interfacial phasc appcared betw een a and B phases in Ti-5Al-2M)-3Zr alloy.Its thickncss could reach 100 nm.The interfacial phase was either single layer structure or double layer structure.The monolithic layer adjacent to B phase was indentified as fcc stru- cture with relationship (110)//(001)m,[111Je//[110Jm The striated layer adja- cent to a phase was indentified as hep with twin relationship {1011)<1012>to a.Thus,the study provided a new cxperimental fact for the controversial topic on structure of striated layer.Chemical composition of interfacial phase varicd slightly with heat treatments,but always belween that of a and B phases. KEY WORDS:phase structure,Ti alloy,heat trcatment During the investigation of phase transformation of the alloy,it was found that interfacial phase appeared betwcen a and B phases after furnace-cooling or air-cooling.Recently,investigation of interfacial phase in titanium alloys has been active and there arc some reviewst1.Three fields of the investigation have been interested in,i.c.(a)appearing conditions or rules of interfacial phaset,31;(b) structure,orientation and formation mechanism of interfacial phaset'1;and (c) effects of interfacial phase on mechanical properties of titanium alloyst7). The interfacial phase may have cither single or double layer structurc.In latter case,the layer adjacent to p is called monolithic layer and that adjacent to u is called striated layer.In Ti-6Al-4V alloy,monolithic layer has been ide- ntificd as fcc lattice with the orientaliont 51:(110)a//(111)m,C111Ja//C110)m,i.e. Kurdjumov-Sachs relationship.In IMI685 alloy,another relationship has been mcasurcdisi:(110)a//(001)m//(0001).,[111)jC110)m//C11207.called fcc I type relationship.For the structure and oricntation of striated layer,there has been controversial.Rhodes and Williamst identified striated layer as 1012 }<1011> Manuscript Rcecived August 11,1989 ··Dcpt,of Material Science and Engincering 568

第 卷第 期 北 京 科 技 大 学 学 报 。 声尸 ， 年 月 一 一 一 ’ “ 邓永 瑞 ‘ “ 。 夕。 ， ‘ 卜东推 秦泽 华 ， ’ ， 、 、、 日 一 一 一 。 ， 夕 · 日 ， 。 ， 〔 〕 ， 〔 〕 。 · 、 、 一 ’ ， ， ‘ 一 ， 日 · 卜 ， ， 尸 认 ， ， 、、 一 日 一 、 〕 一 · ， 认 ’ · 一 几 、 ， ， · · ’ “ ， 毛 ’ ’ 。 、 、 一 ， 。 口 几 、 ‘ 、 一 一 ， ， ， ， 〔 〕 ， 〔 〕 二 ， 一 · 犷 ， 爪 巳 ， 二 。 ， 〔 〕 ， 〔 〕 〔 〕 。 一 · ， · ， ” ‘ 、 ， 立， ， 二 这 一 尹 尹 DOI ：10．13374／j ．issn1001－053x．1989．06．029

twin to a.However,Banerjee et alts101 argued that SAD patterns of Rhodes could be indexed as fcc II type relationship:(111).//(0001).,C110J.//C1120J.. Chenu et altal observed and indexed this fcc II type striated layer in IMI685. However,Margolin et alt21 measured striated layer as 1011}twin hcp to a phase。 In this study for Ti-5Al-2Mo-3Zr alloy,formation condition of interfacial phase,morphologies and structures of monolithic and striated layer,and compo- sition distribution among a,B and interfacial phase have been investigated. 1 Experimental Procedure and Results 1.1 Alloy Composition and Sample Preparation Composition of the studied alloy is shown as follows(wt%): A1-4.91,5.00;Mo-1.85,2.00;Zr-2.65,2.92,Fe-0.062,0.063; C-0.01,0.02,Si-0.01;N-0.0090,0.0092;H-0.0096;0-0.099. The alloy was melted twice in a consumable electrode furnace,forged at 1000C and rolled at 950C.Then,the alloy underwent five different heat trealments respectively.TEM samples were cut to 0.5mm with molybdenum wire electrospark machine and grinded to less than 0.1mm with sand paper.Then. the foils were electro-polished and perforated in an electrolyte HC1O:CHaOH: C2H CH2 CH2OH=1:6:10,at -35C and 10V.Transmission electron microscopes used were EM400T and JOEL100CX. 1.2 TEM Morpho ogy After 950C holding for 1h,the samples of furnace-cooling (F),air-cooling (A)and 800C aging (D)showed interfacial phase between a and B phase,as Fig.1 Interfacial phase after three different heat treatments (a)950C,1h,furnace-cooling.(b)950C,1h,air-cooling. (c)950C,1h,water-quenching plus 800C,4h,air-cooling. 569

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shown in Fig.1.The samples of quenching in water showed primary a aud martensite a';and quenched plus 550C aging showed long B precipitates inside and along boundaries of martensites,but no interfacial phase was observed.For samples of F,A and D,the morphology of interfacia!phase is.saown in Fig.2. Most of the interfacial phase werc dcuble layer structure.The layer adjacent to B was monolithic layer with smooth boundaries and that adjacent to a was striated layer with saw-tooth boundarics.Thickness of the inlerfacial phase could reach 100 nm.Single layer interfacial phase was als,observed as shown in Fig.3 and Fig.4. 0,38m Fig.2 Typical interfacial phase with double structure Fig.3 Dark field of monolithic Fig.4 Dark fleld of striated layea layer(30000×) (60000×) 1.3 Structure and Orientation Fig.5 shows SAD pattern and the corresponding indexed results.It was identified that monolithic layer was fcc with lattice parameter a=0.423 nm and A 570

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the orientation was (110)(001)m,[11//110)m,while a and B conformed to Bargers relationship:(110)a//(0001).,C1113//C1120J..Fig.6.shows SAD pattern of a and striated layer,and the corresponding indexes.The identification snowed that striated layer was hcp with {1011}twin relationship to a phase. 和 000-J Fee(0 002..112 000-110 bcc(110) 0i1 I00 (b) 000 i10 hep(001) (a) Fig.5 SAD pattern of monolithic layer and a,B (a)and corresponding indexing (b) 210m1T1m 012m 000 101m,t 1T1 210 012, (b) (a) Fig.6 SAD pattern of striated layer and a (a)and corresponding indexing (b) 1.4 Ccmpositions of a,8 and interfacial phase EDAX 9100/60 was used to analyse compositions of a,B and interfacial phase. The results were shown in Table. 571

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Table Composltions of a,8 and Interfaclal phase Heat treatments Phases Element F A D Ti 87.152 88.965 88.695 Al 2.441 3.367 2.762 a Mo 7.289 3,367 5.985 Zr 3.118 2.730 2.558 Interfacial Ti 93.458 93.724 92.766 phase Al 3.398 3.706 4.062 Mo 0.164 1.136 0.349 Zr 2.980 2.434 2,283 Ti 93.293 92.960 92.666 Al 4.618 5,158 5.458 B Mo 0 0.064 0 Zr 2.089 1.818 1.878 2 Discussion For Ti-5Al-2Mo-3Zr alloy,interfacial phases with similar morphology were observed in the samples of furnace-cooling,air-cooling and quenching plus 800C aging after 950C holding 1 h.However,the samples of water quenching and quenching plus 550C aging did not show interfacial phase.These results were in agreement with that of Rhodests for Ti-6Al-4V alloy.According to Rhodes, interfacial phase was forming during slow cooling (~28C/h)before 650C and the thickness could reach 400 nm. The monolithic layer in the alloy showed the orientation:(001)m//(110)// (0001).,(110]m//(111)//C1120)..This result was in agreement with that in IMI685 alloyt.According to Banerjeet,this orientation was called fce IA.For Ti-5Al-2Mo-3Zr alloy,however,no evidence showed the existance of fcc II relationship:(111)m//(110)//(0001).,[110]m//C111)a//C1120J.,which was observed by some authorst111. The striated layer of the alloy showed two sets of symmetric <0111>zonc patterns in Fig.7.Thus,it was believed that electron beam was in twin plane but not in twin direction [1s1.The symmetric plane of the two sets of patterns was indentified as (1011),and it must be the twin plane.Therefore,the striated layer was (1011)[1012]twin to a phase.This result was in agree with Margolin et al.in Ti-6Al-2Sn-4Zr-6Mo alloy(+1.Considered that Banerjeet:argued 572

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