材料畢業(yè)設(shè)計(jì)翻譯

1、本科畢業(yè)設(shè)計(jì)（論文）外文參考文獻(xiàn)譯文及原文 學(xué) 院 機(jī)電工程學(xué)院 專 業(yè) 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 （微電子制造裝備及其自動(dòng)化方向）年級班別 2008級（1）班 學(xué) 號 3108000629 學(xué)生姓名 楊慧明 指導(dǎo)教師 熊漢偉 2012年6月-22-目 錄外文參考文獻(xiàn)譯文2原 文11外文參考文獻(xiàn)譯文第三章 材料特性和分析 材料特性是鑒別材料的基礎(chǔ)和用在逆向工程評估性能的一部分。其中在逆向工程中最經(jīng)常被問到的問題是，用什么材料特性評定兩種相同的材料。從理論上說，只有當(dāng)兩種材料的特性被對比并找出相同點(diǎn)后，才可以評定他們是相同的。這樣的成本可能是非常高的，但在技術(shù)上的確是可行的。在工程實(shí)踐中，當(dāng)有足夠

2、的數(shù)據(jù)證明兩個(gè)材料有相關(guān)特性的價(jià)值時(shí)，通常會(huì)認(rèn)為符合了可接受風(fēng)險(xiǎn)的要求。確定相關(guān)的材料特性和當(dāng)量需要全面的了解材料和這種材料制成的部分功能。在逆向工程評估項(xiàng)目中，要想令人信服地解釋有關(guān)材料的性能、屬性、最終拉伸強(qiáng)度，疲勞強(qiáng)度，抗蠕變性，斷裂韌性，工程師需要至少提供以下闡述：1、 特性重要性：解釋相關(guān)的特性對零件的設(shè)計(jì)功能來說是多么重要。2、 風(fēng)險(xiǎn)評估：解釋有關(guān)屬性將如何影響器件的性能，這種材料的屬性如果未能滿足設(shè)計(jì)值會(huì)有什么潛在后果。3、 性能保證：說明對比原始材料，需要進(jìn)行怎樣的測試以顯示其等效性。 本章的主要目的是討論和著重于在逆向工程中材料特性與機(jī)械冶金的應(yīng)用，以幫助讀者完成這些工作任務(wù)

3、。機(jī)械性，冶金性能，物理化學(xué)特性，是進(jìn)行逆向工程機(jī)械中最相關(guān)的材料特性部分。力學(xué)性能是與當(dāng)用力時(shí)彈性和塑性的反應(yīng)有關(guān)。主要力學(xué)性能包括抗拉強(qiáng)度，屈服強(qiáng)度，延展性，抗疲勞，抗蠕變性，應(yīng)力斷裂強(qiáng)度。他們通常反映的應(yīng)力和應(yīng)變之間的關(guān)系。許多力學(xué)性能與冶金性能和物理化學(xué)性質(zhì)密切相關(guān)。 冶金性能是指金屬元素和合金的物理和化學(xué)特性，如合金的微觀結(jié)構(gòu)和化學(xué)成分。這些特性是與熱力學(xué)、動(dòng)力學(xué)過程和通常在這些過程中發(fā)生的化學(xué)反應(yīng)密切相關(guān)的。熱力學(xué)的原理決定當(dāng)兩種元素混合在一起時(shí)能否被結(jié)合成合金成分。動(dòng)力學(xué)過程決定合成的速度。熱力學(xué)的原理常用于建立平衡相圖，這有助于工程師設(shè)計(jì)新的合金和解釋更多的冶金性能和反應(yīng)。它需

4、要一個(gè)很長的時(shí)間才能達(dá)到平衡狀態(tài)。因此，大部分的晶粒形貌和合金結(jié)構(gòu)上的動(dòng)力學(xué)過程取決于反應(yīng)速率，如晶粒的增長速度。 熱處理是一個(gè)過程，被廣泛地使用，通過冶金反應(yīng)獲得最佳的機(jī)械性能。熱處理應(yīng)用于固體無機(jī)非金屬材料，通過加熱和冷卻操作的反復(fù)結(jié)合來獲得合適的組織形態(tài)甚至是理想的特性。最常用的適用于熱處理工藝包括退火處理，固溶處理，老化處理。退火是一個(gè)過程，在特定溫度加熱下一段時(shí)間，然后再慢慢在特定的速度下降溫。它主要用于軟化金屬，提高其可加工性和機(jī)械延展性。適當(dāng)?shù)耐嘶鹨矊⒃黾硬牧蠈用娴姆€(wěn)定性。最常見使用的退火工藝是完全退火，制程退火，等溫退火，球化。當(dāng)退火的唯一目的是為減小壓力，該退火過程通常被稱為

5、消除應(yīng)力。它減少了由鑄造，淬火，正火，加工，冷加工，或焊接引起的內(nèi)部的殘余應(yīng)力。固溶熱處理僅適用于合金，但不適用于純金屬。在這個(gè)過程中，合金被加熱到特定溫度以上，并在此溫度下維持足夠長的時(shí)間，使各組成元素溶合成固溶體，隨后迅速冷卻，以形成固溶體。結(jié)果，這個(gè)過程中產(chǎn)生過飽和，當(dāng)合金冷卻到一個(gè)較低的溫度，其呈熱力學(xué)不穩(wěn)定狀態(tài)，因?yàn)榻M成元素的溶解度隨溫度升高而降低。固溶熱處理往往后續(xù)是老化處理以達(dá)到沉淀硬化。從熱處理角度來看，老化處理描述了某些合金在隨著時(shí)間，溫度變化的特性。這是一個(gè)從過飽和固溶體狀態(tài)變成沉淀的結(jié)果。老化硬化是最重要的強(qiáng)化硬化鋁合金和鎳基合金機(jī)制之一。 物理特性通常是指材料的固有特點(diǎn)

6、。它們是與化工，冶金，機(jī)械過程無關(guān)，如密度，熔融溫度，傳熱系數(shù)，比熱和電導(dǎo)率。材料的這些特性通常是不用任何的機(jī)械力測量。在許多工程應(yīng)用中，這些屬性是至關(guān)重要的。例如，比強(qiáng)度（每單位重量的強(qiáng)度）直接取決于合金的密度，當(dāng)工程師設(shè)計(jì)飛機(jī)和汽車時(shí)它是比絕對抗拉強(qiáng)度更重要。然而，大多數(shù)的材料特性并不是完全獨(dú)立的。他們之間會(huì)互相影響。因此，有些材料特性根據(jù)各自的功能既是機(jī)械特性又是物理特性，如楊氏系數(shù)和剪切系數(shù)。材料的一個(gè)準(zhǔn)確的楊氏系數(shù)通常是由超聲波技術(shù)測量的，而沒有采用任何機(jī)械力。然而，楊氏系數(shù)通常也被稱為應(yīng)力和應(yīng)變之間的比率，它們是在機(jī)械性能評價(jià)的關(guān)鍵要素。冶金和機(jī)械特性之間的相互關(guān)系，也導(dǎo)致一些材料

7、性質(zhì)分為兩類，如硬度和應(yīng)力抗裂性能可以被稱為冶金或機(jī)械性能。3.1合金結(jié)構(gòu)當(dāng)量3.1.1工程合金結(jié)構(gòu)工程合金是工程應(yīng)用中的金屬物質(zhì)，已廣泛應(yīng)用于許多行業(yè)數(shù)百年之久。例如，鋁合金在航空業(yè)中的利用從一開始一直到今天；在1903年，萊特兄弟飛機(jī)的曲軸箱由鋁合金鑄造而成，兩個(gè)或兩個(gè)以上的元素組成的合金是擁有不同的屬性的。當(dāng)它們從液態(tài)冷卻到固態(tài)，大多數(shù)合金會(huì)形成結(jié)晶結(jié)構(gòu)，但沒有結(jié)晶的將會(huì)凝固，像玻璃。金屬玻璃的非晶結(jié)構(gòu)，是一種金屬元素的隨機(jī)布局。相比之下，晶體結(jié)構(gòu)根據(jù)合金元素有一個(gè)反復(fù)的樣式。例如，鋁的晶體結(jié)構(gòu)4%的銅合金是基于鋁與銅原子融合的晶體結(jié)構(gòu)。衡量一種合金的性能如硬度，是它性質(zhì)表現(xiàn)的一部分，和

8、它的晶體結(jié)構(gòu)之下是其獨(dú)特的通用結(jié)構(gòu)。它們都在逆向工程的金屬識別中發(fā)揮著關(guān)鍵的作用。純金屬元素，例如，鋁、銅、和鐵，它們的原子排列具有規(guī)律性。這種原子模式的排序順序最小單位是單元。單個(gè)晶體是這些沒有晶粒邊界的單元在相同方向的聚合。它本質(zhì)上是一個(gè)單一的原子有序排列成的巨大晶粒。這種獨(dú)特的晶體結(jié)構(gòu)，使單晶的力學(xué)性能特別明顯，能夠特殊應(yīng)用。單晶鎳基高溫合金在現(xiàn)代飛機(jī)發(fā)動(dòng)機(jī)渦輪葉片中得到應(yīng)用。第一臺(tái)單晶刃飛機(jī)的發(fā)動(dòng)機(jī)是惠普jt9d-7r4，并在1982年獲得美國聯(lián)邦航空局的認(rèn)證。它應(yīng)用于很多飛機(jī)，例如波音767和空中客機(jī)a310。與對應(yīng)的等軸晶粒對比，一個(gè)單一晶體的噴氣發(fā)動(dòng)機(jī)渦輪機(jī)翼可以抵抗更多次的腐蝕

9、，和好得多的蠕變強(qiáng)度和抗熱疲勞性能。然而，大多數(shù)工程合金，有很多種形態(tài)。晶粒尺寸和其質(zhì)地對其合金性能有很深遠(yuǎn)的影響。細(xì)粒工程合金在室溫下通常具有較高的拉伸強(qiáng)度。然而，對于高溫應(yīng)用，粗晶粒合金由于其耐蠕變性能更好，為首選。微觀結(jié)構(gòu)對于工程合金性能的影響將在后面詳細(xì)討論。3.1.2工藝影響及產(chǎn)品材料的等價(jià)形式從不同的制造工藝和原材料生產(chǎn)的產(chǎn)品形式計(jì)算出結(jié)果的部分功能，特別是獨(dú)特的微觀結(jié)構(gòu)，是廣泛應(yīng)用于確認(rèn)逆向工程材料等效性的特點(diǎn)。傳統(tǒng)的工程合金用于制造過程產(chǎn)生了一種特定的產(chǎn)品形式包括鑄造，鍛造，軋制，以為其他冷熱工作。粉末冶金快速凝固，化學(xué)氣相沉積法，以及許多其他特殊工藝，例如，魚鷹噴射成形和超塑

10、性成形，也可用于針對特定應(yīng)用的行業(yè)。一些近凈型的過程，直接塑造成接近最終產(chǎn)品的形式或幾何形狀復(fù)雜的合金。在具有多個(gè)處理步驟的傳統(tǒng)鑄造和鍛造產(chǎn)品中，從原材料到最終產(chǎn)品涉及較少步驟的簡單轉(zhuǎn)換往往是更可取的。例如，“魚鷹”噴射成型過程霧化熔融的合金，形成一個(gè)環(huán)型的瓶坯硬件或密封的如發(fā)動(dòng)機(jī)渦輪。近凈型預(yù)制棒接著通過熱等靜壓機(jī)制成最終的產(chǎn)品。一個(gè)魚鷹噴射成形7a60合金鎳基合金產(chǎn)品更具成本效益，它通常有一個(gè)約65微米的平均晶粒尺寸。它顯示了一個(gè)類似的微觀結(jié)構(gòu)和可比物業(yè)鍛造件具有相同的合金成分，并比鑄造產(chǎn)品具有更好的性能。制造技術(shù)的最新進(jìn)展中，生產(chǎn)了顯微結(jié)構(gòu)和納米合金。工程合金的力學(xué)性能主要取決于兩個(gè)要素

11、：組成和微觀結(jié)構(gòu)。盡管合金成分有特定的結(jié)構(gòu)，但是微觀結(jié)構(gòu)在這過程中不斷發(fā)展。因此，不同產(chǎn)品中工程合金的結(jié)構(gòu)和力學(xué)性能是截然不同的。圖3.1顯示了鋁合金鑄件的晶粒結(jié)構(gòu)。 （a）（b）圖3.1 這在鋁合金擠壓成型中能觀察到很不同的微觀結(jié)構(gòu)，如圖3.1b所示，盡管這兩者有相同的合金成分：鋁-3.78%，銅-1.63%，鋰-1.40%。不用多說，鑄鋁和擠壓鋁箔也一樣有非常不同的特性。在逆向工程中，該微觀結(jié)構(gòu)在零件的制造過程中提供了重要的信息。3.2 物相的定性與定量 相圖是根據(jù)相變過程建立起來的。它說明了合金成分，相位和溫度之間的關(guān)系。它提供了各種制造和熱處理工藝的參考指南。從相圖中提取的信息對物相鑒

12、定起了重要作用，因此它在逆向工程中對制造工藝和熱處理驗(yàn)證也是至關(guān)重要的。本節(jié)將討論相圖和熱力學(xué)和動(dòng)力學(xué)的相關(guān)理論的基礎(chǔ)。3.2.1 相圖 合金相圖是一個(gè)冶金插圖，顯示熔化和凝固溫度以及合金在特定溫度下的不同階段。平衡相圖顯示了各平衡相的函數(shù)成分和溫度。根據(jù)推定，動(dòng)力學(xué)反應(yīng)過程在每一步是足夠快地達(dá)到平衡狀態(tài)。這本書中，除了另有指明之外，下面所有的相圖都指的是平衡相圖。圖3.2只是是一個(gè)部分的鐵碳相圖（fe-c），因?yàn)檫@個(gè)圖非常復(fù)雜所以無法全部完成。相圖的y軸是溫度，x軸表示合金元素組成量。二元fe-c相圖中，鐵是主要的基本元素，碳是合金元素。最左邊的y軸代表純鐵，也就是100的鐵。溫度鐵 碳的百

13、分含量圖3.2 部分的fe-c相示意圖。圖的橫坐標(biāo)從左到右增加含碳量。合金元素的單位通常是百分比含量，但偶爾使用原子百分比含量。有時(shí)在圖的底部或頂部標(biāo)記百分點(diǎn)符號。圖3.2中顯示的碳含量范圍從0到6.7。含碳量6.7的 fe是一種金屬互化物，碳化鐵。合金的各構(gòu)成要素可能由范圍固定的或窄的成分合并成一個(gè)獨(dú)特的復(fù)合合金。這些化合物是金屬化合物。大多數(shù)金屬化合物有自己的特性，有特定的成分和獨(dú)特的晶體結(jié)構(gòu)及性能。碳化鐵fe3c，是有色鐵碳合金中最常見的金屬化合物。大多數(shù)的fe-c二元相圖是fe-fe3c相圖，用fe3c而不是100純碳作基線圖。j.威拉德吉布斯相律和熱力學(xué)法例相律指導(dǎo)金屬相變相關(guān)知識。

14、吉布斯相律通過數(shù)學(xué)公式3.1描述，其中f是自由或獨(dú)立變量，c是元素?cái)?shù)量，而p是在熱力學(xué)平衡系統(tǒng)中的相數(shù)。 f = c p + 2 (3.1)典型的獨(dú)立變量是溫度和壓力。大多數(shù)相圖假設(shè)在大氣壓力下。當(dāng)合金熔化，固體和液體并存，因此，p =2。吉布斯相律只允許在純金屬中有一個(gè)獨(dú)立變量，其中c= 1。這說明，在大氣壓力下，純金屬在一個(gè)特定的熔融溫度下熔化以及一個(gè)固定的沸點(diǎn)下沸騰。例如，在圖3.2中純鐵的熔化溫度標(biāo)記為1534c。然而，二元合金，其中c= 2，吉布斯相律允許更多的獨(dú)立變量。對于一個(gè)給定的組成，二元合金的液固相變溫度是在一定的溫度范圍內(nèi)，而不是某一個(gè)固定的溫度。圖3.2所示，在1,400

15、c，fe-3c二元合金是均勻的液體狀態(tài)。當(dāng)溫度降低到液相溫度以下（1300c左右）它會(huì)開始凝固。在相圖中液相是存在于液體開始凝固的溫度邊界內(nèi)。換句話說，液相開始與各種成分的合金熔化溫度。在圖3.2中，液相表示由1534c時(shí)的純液態(tài)鐵融化溫度曲線持續(xù)到1147c時(shí)的fe-4.3c熔融溫度曲線之間. fe-4.3c被定義為共晶成分。盡管這是一個(gè)二元合金，但是它是在1147c這個(gè)固定的溫度融化，因?yàn)檫@兩個(gè)不同的固相能在同一溫度凝固。如圖3.2所示，共晶溫度是最低的鐵碳合金熔化溫度。完成凝固溫度的曲線被定義為固相線。上述合金的液相是均勻的液體狀態(tài)，它通常被稱為液相或液體溶液，并在許多相圖中標(biāo)記為l。下

16、面的合金固相線是一個(gè)均勻的固態(tài)，這通常被稱為作為固相或固溶體。各種合金的固相通常用指定的希臘字母，從左邊開始表示相，繼續(xù)由相圖右移，按順序地表示，相。對于 fe3 %c合金，新形成的固相和剩余的液體，在1147c的固相和液相之間共存。fe3% c合金隨著溫度的不斷降低相繼被轉(zhuǎn)化成不同固相，由相向混合了fe3c的相轉(zhuǎn)化。因此，熔融合金將從均勻相液體狀態(tài)凝固成多種固相狀態(tài)，在凝固過程中每種形態(tài)的轉(zhuǎn)變是一步步連續(xù)地進(jìn)行的。在特定溫度下的每種相可以根據(jù)杠桿原理進(jìn)行定量分析。相圖上說明了一切相變，并給工程師們提供了寶貴的“足跡”，讓他們回溯在進(jìn)行逆向工程中的一部分原始經(jīng)歷。熱力學(xué)的原理可以從理論上推測的

17、平衡相圖中的相的存在。然而，它可能需要很長時(shí)間來解釋相變原理。相的形成速度和機(jī)制是由動(dòng)力學(xué)原理指出和解釋的，動(dòng)力學(xué)原理也解釋了許多非平衡相變原理。各種非平衡相變圖被用于許多工程應(yīng)用中，通過控制溫度的變化率以創(chuàng)建特定的非平衡相。例如，鐵合金持續(xù)的冷卻曲線被廣泛應(yīng)用于熱處理工業(yè)。從逆向工程的角度來看，這些持續(xù)的冷卻曲線往往比平衡相圖提供更實(shí)用的信息。大多數(shù)工程合金中含有兩個(gè)以上的合金元素。如果有三個(gè)組成元素，它則被稱為三元體系。三元相圖是一個(gè)三維空間棱鏡，溫度軸被垂直地建立在組成的三角基面之上，每一面代表一個(gè)元素。這是立體相圖，由三個(gè)二元相圖建成，每面一個(gè)二元相圖。3.2.2 等效晶粒形態(tài) 最常見

18、的三種金屬的微觀結(jié)構(gòu)晶粒形貌是等軸晶，與樹突狀鑄件結(jié)構(gòu)混合的柱狀，和單晶。在等軸晶微觀結(jié)構(gòu)中，如圖3.1a所示，在所有軸的方向上具有大致相當(dāng)?shù)某叽?。在鑄件凝固過程中，柱狀結(jié)構(gòu)通常從寒冷的模具表面開始成形，并逐漸向內(nèi)部移動(dòng)，形成粗大的柱狀晶粒形貌。柱狀結(jié)構(gòu)通常在最后會(huì)被混合在樹突狀鑄件結(jié)構(gòu)中。單晶沒有相鄰的形態(tài)和沒有晶粒邊界；整個(gè)晶體在一個(gè)晶體方向?qū)R。圖3.3然而，這些基本晶粒的形態(tài)將通過動(dòng)力學(xué)過程演變成更復(fù)雜的結(jié)構(gòu)。例如，再晶粒和晶粒的變化。其他衍生的微觀結(jié)構(gòu)是在成形制品的具體工藝中體現(xiàn)出來的。例如，冷或熱的圖紙可以產(chǎn)生顆粒在一個(gè)方向上一字排開的高度定向質(zhì)感的微觀結(jié)構(gòu)。圖3.3顯示了高方向的

19、鎢絲質(zhì)感的微觀結(jié)構(gòu)。在逆向工程中，復(fù)制的部分晶粒形貌至關(guān)重要的兩個(gè)原因如下：首先，材料的性能和部分功能很大程度上取決于微觀結(jié)構(gòu)；其次，晶體的形態(tài)給制造工藝和熱處理工藝提供了關(guān)鍵的信息。不同的熱處理工藝，有不同的制造工藝呈現(xiàn)出不同的晶粒形貌，并具有不同的力學(xué)性能。原 文3. material characteristics and analysis material characteristics are the cornerstone for material identification and performance evaluation of a part made using reve

20、rse engineering. one of the most frequently asked questions in reverse engineering is what material characteristics should be evaluated to ensure the equivalency of two materi-als. theoretically speaking, we can claim two materials are “the same” only when all their characteristics have been compare

21、d and found equivalent. this can be prohibitively expensive, and might be technically impossible. in engineering practice, when sufficient data have demonstrated that both the materials having equivalent values of relevant characteristics will usually deem having met the requirements with acceptable

22、 risk. the determination of relevant material characteristics and their equivalency requires a comprehensive understanding of the material and the functionality of the part that was made of this material. to convincingly argue which properties, ultimate tensile strength, fatigue strength, creep resi

23、stance, or fracture toughness, are relevant material properties that need to be evaluated in a reverse engineering project, the engineer needs at least to provide the following elaboration: 1. property criticality: explain how critical this relevant property is to the parts design functionality. 2.

24、risk assessment: explain how this relevant property will affect the part performance, and what will be the potential consequence if this material property fails to meet the design value. 3. performance assurance: explain what tests are required to show the equivalency to the original material. the p

25、rimary objective of this chapter is to discuss the material characteristics with a focus on mechanical metallurgy applicable in reverse engineering to help readers accomplish these tasks. the mechanical, metallurgical, and physical properties are the most relevant material properties to reverse engi

26、neer a mechanical part. the mechanical properties are associated with the elastic and plastic reactions that occur when force is applied. the primary mechanical properties include ultimate tensile strength, yield strength, ductility, fatigue endurance, creep resistance, and stress rupture strength.

27、they usually reflect the relationship between stress and strain. many mechanical properties are closely related to the metallurgical and physical properties. the metallurgical properties refer to the physical and chemical characteristics of metallic elements and alloys, such as the alloy microstruct

28、ure and chemical composition.these characteristics are closely related to the thermodynamic and kinetic processes, and chemical reactions usually occur during these processes. the principles of thermodynamics determine whether a constituent phase in an alloy will ever be formulated from two elements

29、 when they are mixed together. the kinetic process determines how quickly this constituent phase can be formulated. the principles of thermodynamics are used to establish the equilibrium phase diagram that helps engineers to design new alloys and interpret many metallurgical properties and reactions

30、. it takes a very long time to reach the equilibrium condition. therefore, most grain morphologies and alloy structures depend on a kinetic process that determines reaction rate, such as grain growth rate.heat treatment is a process that is widely used to obtain the optimal mechanical properties thr

31、ough metallurgical reactions. it is a combination of heating and cooling operations applied to solid metallic materials to obtain proper microstructure morphology, and therefore desired properties. the most commonly applied heat treatment processes include annealing, solution heat treatment, and agi

32、ng treatment. annealing is a process consisting of heating to and holding at a specified temperature for a period of time, and then slowly cooling down at a specific rate. it is used primarily to soften the metals to improve machinability, workability, and mechanical ductility. proper annealing will

33、 also increase the stability of part dimensions. the most frequently utilized annealing processes are full annealing, process annealing, isother-mal annealing, and spheroidizing. when the only purpose of annealing is for the relief of stress, the annealing process is usually referred to as stress re

34、lieving. it reduces the internal residual stresses in a part induced by casting, quenching, normalizing, machining, cold working, or welding. solution heat treatment only applies to alloys, but not pure metals. in this process an alloy is heated to above a specific temperature and held at this tempe

35、rature for a sufficiently long period of time to allow a constituent element to dissolve into the solid solution, followed by rapid cooling to keep the constituent element in solution. consequently, this process produces a supersaturated, thermodynamically unstable state when the alloy is cooled dow

36、n to a lower temperature because the solubility of the constituent element decreases with temperature. the solution heat treatment is often followed by a subsequent age treatment for precipitation hardening. from the heat treatment perspective, aging describes a time-temperature-dependent change in

37、the properties of certain alloys. it is a result of precipitation from a supersaturated solid solution. age hardening is one of the most important strengthening mechanismsfor precipitation-hardenable aluminum alloys and nickel-base superalloys.physical properties usually refer to the inherent charac

38、teristics of a material. they are independent of the chemical, metallurgical, and mechanical processes, such as the density, melting temperature, heat transfer coefficient, specific heat, and electrical conductivity. these properties are usually measured without applying any mechanical force to the

39、material. these properties are crucial in many engineering applications. for example, the specific tensile strength (strength per unit weight) directly depends on alloy density, and it is more important than the absolute tensile strength when engineers design the aircraft and automobile. however, mo

40、st material characteristics do not stand alone. they will either affect or be affected by other properties. as a result, some material properties fall into both mechanical and physical property categories, depending on their functionality, such as youngs modulus and shear modulus. an accurate youngs

41、 modulus is usually measured by an ultrasonic technology without applying any mechanical force to the material. however, youngs modulus is also commonly referred as a ratio between the stress and strain, and they are the key elements in mechanical property evaluation. the interrelationships between

42、metallurgical and mechanical behaviors also cause some material properties to fall into both categories, such as hardness and stress corrosion cracking resistance can be referred to as either metallurgical or mechanical properties.3.1 alloy structure equivalency 3.1.1 structure of engineering alloys

43、 engineering alloys are metallic substances for engineering applications, and have been widely used in many industries for centuries. for example, the utilization of aluminum alloys in the aviation industry started from the beginning and continues to today; the crankcase of the wright brothers airpl

44、ane was made of cast aluminum alloy in 1903. alloys are composed of two or more elements that possess properties different from those of their constituents. when they are cooled from the liquid state into the solid state, most alloys will form a crystalline structure, but others will solidify withou

45、t crystallization to stay amorphous, like glass. the amorphous structure of metallic glass is a random layout of alloying elements. in contrast, a crystalline structure has a repetitive pattern based on the alloying elements. for instance, the crystalline structure of an aluminum4% copper alloy is b

46、ased on the crystal structure of aluminum with copper atoms blended in. the measurable properties of an alloy such as hardness are part of its apparent character, and the underneath crystallographic structure is its distinctive generic structure. both play their respective critical roles in alloy id

47、entification in reverse engineering. pure metallic elements, for example, aluminum, copper, or iron, usually have atoms that fit in a few symmetric patterns. the smallest repetitive unit of this atomic pattern is the unit cell. a single crystal is an aggregate of these unit cells that have the same

48、orientation and no grain boundary. it is essentially a single giant grain with an orderly array of atoms. this uniquecrystallographic structure gives a single crystal exceptional mechanical strength, and special applications. the single-crystal ni-base superalloy has been developed for turbine blade

49、s and vanes in modern aircraft engines. the first single-crystal-bladed aircraft engine was the pratt & whitney jt9d-7r4, which received faa certification in 1982. it powers many aircraft, such as the boeing 767 and the airbus a310. compared to the counterpart with equiaxed grains, a single-crystal

50、jet engine turbine airfoil can have multiple times better corrosion resistance, and much better creep strength and thermal fatigue resistance. most engineering alloys, however, have a multigrain morphology. the grain size and its texture have profound effects on alloy properties. fine grain engineer

51、ing alloys usually have higher tensile strength at ambient temperature. however, for high-temperature applications, coarse grain alloys are preferred due to their better creep resistance. the effects of microstructure on the properties of engineering alloys will be discussed in detail later.3.1.2 ef

52、fects of process and product form on material equivalency the part features, distinctive microstructure in particular, resulted from dif- ferent manufacturing processes, and product forms thereby produced from raw materials are the characteristics widely used to identify material equivalency in reve

53、rse engineering. conventional manufacturing processes used on engineering alloys to produce a specific product form include casting, forging, and rolling, as well as other hot and cold work. power metallurgy, rapid solidification, chemical vapor deposition, and many other special processes, for exam

54、ple, osprey spray forming and superplastic forming, are also used in industries for specific applications. some near-net-shape processes directly shape the alloy into the near-final product form or complex geometry. in comparison to traditional cast and wrought products with multiple processing step

55、s, a simpler conversion from raw material to the final product that involves fewer steps is often more desirable. for example, the osprey spray forming process first atomizes a molten alloy, which is then sprayed onto a rotating mendrel to form a ring-shape preform hardware like an engine turbine ca

56、se or seal. the near-net-shape preform is subsequently made into the final product using a hot isostatic press. an osprey sprayformed ni-base superalloy product is more cost effective, and typically has an average grain size of about 65 m. it shows a similar microstructure and comparable properties

57、to a wrought piece with the same alloy composition, and has better properties than a cast product. recent advances in manufacturing technologies have also produced alloys with nano-microstructure. the mechanical properties of engineering alloys are primarily determined by two factors: composition and microstructure. though the alloy composition is intrinsic by design, the microstructure evolves during manufacturing. the microstructure and consequently the mechanical properties