【文章內(nèi)容簡(jiǎn)介】 中不可替代的分量。 致謝在此，首先要感謝我尊敬的指導(dǎo)老師劉劍老師，本文是在劉老師的悉心指導(dǎo)下完成的。在畢業(yè)設(shè)計(jì)期間，劉老師給予了我很大的幫助和教導(dǎo)。從論文的選定到實(shí)驗(yàn)研究，從資料收集到方案確定，劉老師都給了我大量的中肯的建議和意見(jiàn)，正是由于劉老師的悉心指導(dǎo)，我的畢業(yè)設(shè)計(jì)得以順利完成。在此表達(dá)我對(duì)劉劍老師的感激之情。我還要感謝在四年大學(xué)學(xué)習(xí)生涯中，傳授我知識(shí)的每一位老師，是你們教會(huì)了我很多知識(shí)和做人的道理，正是你們的言傳身教，在一定意義上幫助我順利完成了本次畢業(yè)設(shè)計(jì)。再次向全體老師表示衷心的謝意！同時(shí)，我還得感謝在我的大學(xué)四年求學(xué)中，傳授給我知識(shí)的老師們，正是你們無(wú)私的傳道授業(yè)解惑精神，使我有了良好的專(zhuān)業(yè)知識(shí)，從而也使我的畢業(yè)設(shè)計(jì)得以順利完成。我還要感謝在我的畢業(yè)設(shè)計(jì)過(guò)程中，幫助我的同學(xué)以及室友們，正是通過(guò)問(wèn)題的交流探討，使我遇到的困惑得到明朗。以及室友們共同營(yíng)造的畢業(yè)設(shè)計(jì)的積極氛圍，在一定程度上也使得我的畢業(yè)設(shè)計(jì)順利完成。 最后，謹(jǐn)向百忙之中審閱論文和參加答辯的每一位老師表示由衷的謝意！ 參考文獻(xiàn)：[1]洪蕾，吳剛，激光制造技術(shù)基礎(chǔ)[M]，北京：人民交通出版社，,120[2]史玉升，激光制造技術(shù)[M]，北京：機(jī)械工業(yè)出版社，,89[3]左鐵釧，21世紀(jì)的先進(jìn)制造:激光技術(shù)與工程[M]，北京：科學(xué)出版社，2007,18[4]陳繼民，徐向陽(yáng)，肖榮詩(shī)，激光現(xiàn)代制造技術(shù)[M]，北京：國(guó)防工業(yè)出版社，,89[5]（德）浦諾威（Poprawe,R.）著，張冬云譯，激光制造工藝：基礎(chǔ)、展望和創(chuàng)新應(yīng)用實(shí)例[M]，北京：清華大學(xué)出版社，115117[6]曹鳳國(guó)，激光加工技術(shù)[M]，北京：北京科學(xué)技術(shù)出版社，,16[7]劉順洪，激光制造技術(shù)[M]，武漢:華中科技大學(xué)出版社，6197[8]黃衛(wèi)東，激光立體成型[M]，西安：西北工業(yè)大學(xué)出版社，,244283[9]（日）金岡優(yōu)，激光加工[M]，北京，機(jī)械工業(yè)出版社，,2225[10]虞剛，虞和濟(jì)，集成化激光智能加工工程[M]，北京：冶金工業(yè)出版社，96103[11] 王揚(yáng),吳雪峰,[J].航空制造技術(shù),2011,(第8期).[12]謝翼江，郭勁，劉喜明，激光加工技術(shù)及其應(yīng)用[M]，北京：科學(xué)出版社，2012,106163[13] 郭偉強(qiáng),[J].科協(xié)論壇(下半月),2011,(第4期).[14]關(guān)振中，激光加工工藝手冊(cè)[M]，北京：中國(guó)計(jì)量出版社，,122146[15] Vicente Afonso Ventrella。Jos233。 Roberto Berretta。Wagner de Rossi. 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Journal of Physics: Conference Series, 2012, : 012002附錄1 英文原文Development of Weld Metal Microstructures in Pulsed Laser Welding of Duplex Stainless Steel F. Mirakhorli, F. Malek Ghaini, and . Torkamany (Submitted October 30, 2011) The microstructure of the weld metal of a duplex stainless steel made with Nd:YAG pulsed laser is investigated at different travel speeds and pulse frequencies. In terms of the solidi?cation pattern, the weld microstructure is shown to be posed of two distinct zones. The presence of two peting heat transfer channels to the relatively cooler base metal and the relatively hotter previous weld spot is proposed to develop two zones. At high overlapping factors, an array of continuous axial grains at the weld centerline is formed. At low overlapping factors, in the zone of higher cooling rate, a higher percentage of ferrite is transformed to austenite. This is shown to be because with extreme cooling rates involved in pulsed laser welding with low overlapping, the ferritetoaustenite transformation can be limited only to the grain boundaries.Keywords duplex stainless steel, microstructure, pulsed laser welding, solidi?cationIntroduction　　Duplex stainless steels (DSS) are widely used in petro chemical and chemical processings because of the bination of corrosion resistance and advantageous mechanical proper ties. The wrought alloys microstructure at room temperature is posed of austenite and ferrite phases (Ref 1, 2). However, the microstructure resulting from a fusion welding process can be signi?cantly different because of the cooling rates involved (Ref 35). Figure 1 depicts a typical DSS alloy that would solidify pletely into ferrite and then, while cooling through solid state transformation, it partially transforms into austenite (Ref 1, 2). Considering the paratively higher cooling rates involved in welding processes, the weld metal and the HAZ microstructure could contain higher amounts of ferrite phase than the base metal. This also can affect the mechanical and corrosion resistance properties of DSS welds (Ref 27).　　Welding DSS alloys with continuous power laser has been the subject of previous research studies (Ref 810). It is shownthat the low heat input and consequently high cooling rates canlead to the formation of higher a/c ratio. On the other hand, pulsed laser can provide further controls on power and heat input. However, there can be questions on how the microstruc ture of a DSS alloy is affected by the rapid pulsating nature of the heat source, since consecutive melting and solidi?cation of weld spots would occur (Ref 1113).In the present study, the focus is on the evaluation of the microstructure in different regions in the weld metal of a DSS and also analyzing the effect of variation in weld travel speed and pulse frequency.Experimental Procedure　　Bead