非晶合金的原子排布是短程有序和長(zhǎng)程無(wú)序，具有高硬度、高強(qiáng)度和大彈性極限等力學(xué)性能[1] 塊狀非晶合金是一種具有極大應(yīng)用前景的候選生物醫(yī)用材料[2] 傳統(tǒng)晶態(tài)金屬材料的楊氏模量是人體骨骼組織的10~20倍，植入人體后與骨骼模量不匹配，使骨骼負(fù)荷不足，產(chǎn)生“應(yīng)力屏蔽”而引起骨質(zhì)疏松，不利于骨愈合 非晶合金的楊氏模量較低、彈性極限較高，能隨著骨骼的自然彎曲而彈性彎曲，使應(yīng)力分布更加均勻，減弱了應(yīng)力屏蔽效應(yīng)，可提高骨組織的愈合速率[3]

鈦基非晶合金兼具鈦合金和非晶合金的特點(diǎn)，其密度低、生物相容性良好[4]、耐蝕性高[5]和與骨組織楊氏模量匹配[6]，有廣闊的應(yīng)用前景[7] Zhu等[8]用Pd元素替代Ti-Ni-Cu和Ti-Zr-Cu-Ni非晶合金體系中具有細(xì)胞毒性的Ni元素，研發(fā)出一種新型Ti-Zr-Cu-Pd 4元非晶合金體系 與傳統(tǒng)的Ti基非晶合金相比，該體系不含Ni、Al和Be等有毒元素，更適用于生物醫(yī)用領(lǐng)域 這個(gè)體系中的Ti40Zr10Cu36Pd14(原子比，下同)其臨界尺寸達(dá)到7 mm，晶化焓為287.6 kJ/mol，具有很高的玻璃形成能力和熱穩(wěn)定性

在非晶合金的室溫變形過(guò)程中發(fā)生一種特有的剪切局域化和應(yīng)變軟化，使其室溫塑性極低[9] 研究表明，在非晶基體中引入塑性晶化增強(qiáng)相可提高其室溫塑性 [10] Ti合金中的Mo元素是一種重要的β-Ti相穩(wěn)定化元素，能細(xì)化鈦合金晶粒，使β鈦合金的穩(wěn)定性和強(qiáng)度提高[11] Mo不僅易與Zr或Ti生成無(wú)限固溶體，還能顯著降低β/(α + β)相變溫度并擴(kuò)展β相穩(wěn)定區(qū)域[12~14] 本文在非晶形成能力較高、且不含有毒性元素的Ti40Zr10Cu36Pd14非晶合金中微添加Mo元素，使其在凝固過(guò)程中原位析出內(nèi)生塑性β-Ti相，研究不同Mo添加量合金的組織和力學(xué)性能

1 實(shí)驗(yàn)方法

實(shí)驗(yàn)用塊體合金原料Ti、Zr、Cu、Pd和Mo的純度高于99.99% (質(zhì)量分?jǐn)?shù)) 按照(Ti0.4Zr0.1Cu0.36Pd0.14)100 - x Mo x (x =0，1，2，5，原子分?jǐn)?shù)，分別記為Mo0，Mo1，Mo2，Mo5)配料，在熔融Ti錠吸氧和高純氬氣(> 99.999%，質(zhì)量分?jǐn)?shù))保護(hù)下用電弧爐熔煉母合金 為了確保母合金錠的成分均勻，合金錠反復(fù)熔煉至少5次 將煉好的合金錠破碎并清洗后裝入石英管，用銅模噴鑄法制備出直徑為2 mm的棒狀試樣

用XRD-7000型X射線衍射儀(XRD，CuKα )分析棒狀試樣的相組成，用GeminiSEM300場(chǎng)發(fā)射掃描電子顯微鏡觀察試樣的微觀組織和斷口形貌 用Zwick Z020型萬(wàn)能材料試驗(yàn)機(jī)進(jìn)行壓縮實(shí)驗(yàn)，試樣的長(zhǎng)徑比為2∶1，將其兩端面磨平并使其垂直于受力方向，應(yīng)變速率為5.0 × 10-4 s-1

2 結(jié)果和討論2.1 微觀組織

圖1給出了4種不同Mo含量的Ti基非晶復(fù)合材料試樣的XRD譜 可以看出，在Mo0試樣(沒(méi)添加Mo元素)和Mo1試樣(添加1%Mo)的譜中只有一個(gè)明顯的彌散非晶衍射峰，沒(méi)有出現(xiàn)晶體峰 而在Mo2與Mo5樣品的譜中除了非晶衍射峰，還出現(xiàn)了尖銳的晶化峰(標(biāo)定為β-Ti相) 這表明，在Mo2和Mo5中析出了β-Ti相 從XRD譜中還可見(jiàn)，隨著Mo含量的提高β-Ti相的衍射峰強(qiáng)度逐漸提高，表明樣品中β-Ti的含量隨之提高

圖1



圖1Ti基非晶復(fù)合材料的XRD譜

Fig.1XRD patterns of Ti-based amorphous composites

圖2給出了Mo0、Mo1和Mo2試樣的SEM圖像 從圖2a和圖2b可見(jiàn)，Mo0和Mo1試樣由沒(méi)有明顯對(duì)比的均勻非晶相組成，沒(méi)有生成晶化相，與圖1中XRD譜給出的結(jié)果一致；而在圖2c(Mo2)中除了非晶基體還有點(diǎn)狀的析出相，但是因析出相的成分與基體相近而對(duì)比度不高 因此，對(duì)Mo2進(jìn)行了Mo元素的面掃 在圖2d中可清晰觀察到析出相的形貌，圖像分析結(jié)果給出β-Ti相的體積分?jǐn)?shù)約為10%，平均尺寸約為8 μm

圖2



圖2不同Mo含量樣品的SEM照片和Mo元素的分布

Fig.2SEM images of samples at different Mo contents (a) Mo0; (b) Mo1; (c) Mo2 and (d) distribution of Mo element in (c) -plot

上述結(jié)果表明，由于Mo在Ti中的固溶度較高，當(dāng)添加量≤ 1%時(shí)Mo元素全部固溶進(jìn)入基體，難以促進(jìn)β-Ti相的析出 當(dāng)Mo添加量≥ 2%時(shí)在非晶基體中析出β-Ti相，生成原位自生鈦基非晶復(fù)合材料且β-Ti相彌散均勻分布

為了提高樣品中β-Ti相的體積分?jǐn)?shù)，制備了Mo5試樣(Mo元素的含量為5%)，其SEM照片和對(duì)應(yīng)的元素面掃圖像如圖3所示 由圖3a可以看出，隨著Mo含量的提高M(jìn)o5中的β-Ti相的體積分?jǐn)?shù)隨之提高且尺寸更大 分析結(jié)果給出了Mo5中β-Ti相的體積分?jǐn)?shù)為20%，平均尺寸為15 μm 圖3b~f中的元素面掃分布結(jié)果表明，復(fù)合材料中的非晶基體由均勻分布的Ti、Zr、Cu和Pd 4種元素組成，析出的β-Ti相則主要由Ti和Mo元素組成

圖3



圖3Mo5試樣的SEM照片對(duì)應(yīng)的元素面掃圖

Fig.3SEM images of Mo5 specimens (a) and corresponding elemental face sweeps of Ti (b), Zr (c), Cu (d), Pd (e) and Mo (f)

2.2 力學(xué)性能

圖4給出了不同Mo添加量樣品的壓縮真應(yīng)力-真應(yīng)變曲線，可見(jiàn)所有試樣均表現(xiàn)出一定的塑性變形量，而Mo2和Mo5出現(xiàn)了明顯的加工硬化現(xiàn)象 隨著Mo含量的提高試樣的斷裂強(qiáng)度和塑性均隨之提高 不含Mo的基體合金其斷裂強(qiáng)度為1992 MPa，壓縮塑性為1.2%；Mo1的斷裂強(qiáng)度為2057 MPa，比基體提高了3.3%，塑性為1.7%，比基體有所提高；Mo2和Mo5的斷裂強(qiáng)度分別為2422和2630 MPa，塑性分別為3.9%和7.3%，強(qiáng)度比基體分別提高了21.6%和32.0%，塑性比基體分別提高了2.25倍和5.08倍(表1) 上述結(jié)果表明，Ti基非晶基體中β-Ti相的析出顯著提高了非晶復(fù)合材料的室溫壓縮性能，且β-Ti相的體積分?jǐn)?shù)越高其增強(qiáng)效果越顯著

圖4



圖4不同Mo含量試樣的室溫壓縮真應(yīng)力-應(yīng)變曲線

Fig.4Room temperature compression true stress-strain curves for specimens with different Mo contents

Table 1

表1

表1不同Mo含量的Ti基非晶復(fù)合材料的楊氏模量E、斷裂強(qiáng)度σf、屈服強(qiáng)度σy、斷裂應(yīng)變?chǔ)舊、屈服應(yīng)變?chǔ)舙和加工硬化指數(shù)n

Table 1Young′s modulus E, fracture strength σf, yield strength σy, fracture strain εf, yield strain εp and work hardening index n of Ti-based amorphous composites with different Mo contents

Sample	E / GPa	σf / MPa	σy / MPa	εf / %	εp / %	n
Mo0	122	1992	1850	2.7	1.2	-
Mo1	128	2057	1912	3.2	1.7	-
Mo2	113	2422	1818	5.5	3.9	0.14
Mo5	105	2630	1772	9.0	7.3	0.20

非晶復(fù)合材料在室溫加載時(shí)其中的韌性第二相先屈服變形，隨著應(yīng)力的增大基體中的剪切帶形核并擴(kuò)展[15] 基體中的剪切帶在擴(kuò)展過(guò)程中可能繞過(guò)韌性相產(chǎn)生分枝或在與第二相的界面停止擴(kuò)展，也可能在界面增殖生成二次剪切帶，最終形成多重剪切帶[16] 每條剪切帶對(duì)應(yīng)部分塑性變形量，多重剪切帶的生成使復(fù)合材料的塑性提高，避免了基體內(nèi)部高度局域化的剪切帶失穩(wěn)轉(zhuǎn)變?yōu)榧羟袔Фl(fā)生脆性斷裂[17] 為了進(jìn)一步探究不同Mo添加量非晶復(fù)合材料的變形機(jī)理，對(duì)比了Mo0和Mo5試樣的壓縮斷口SEM照片(圖5) 圖5a、b給出了Mo0試樣的斷口SEM圖像 可以看出，在試樣側(cè)面產(chǎn)生了與斷面平行的剪切帶，但是數(shù)量較少，且斷面呈非晶合金典型的河流狀花樣[18] 圖5c、d給出了Mo5試樣的斷口SEM圖像，可見(jiàn)比Mo0斷裂后側(cè)面產(chǎn)生的剪切帶更為明顯、數(shù)量更多，還產(chǎn)生了大量垂直于斷裂方向的二次剪切帶 這表明，在變形過(guò)程中剪切帶的擴(kuò)展受到原位β-Ti相的阻礙而發(fā)生偏轉(zhuǎn)或增殖 Mo5斷面不僅呈現(xiàn)出非晶合金經(jīng)典的河流狀花樣，還存在大片局部熔化區(qū)與β-Ti相，表明剪切帶與第二相發(fā)生了強(qiáng)烈的交互作用 在非晶復(fù)合材料中存在一種特征值，稱(chēng)為加工區(qū)域尺寸(Processing zone)[19] 復(fù)合組織中第二相的尺寸和相間距越接近此加工區(qū)域的尺寸，復(fù)合材料的力學(xué)性能越優(yōu)異，這與基體內(nèi)裂紋前端的張開(kāi)位移有關(guān) 研究表明，Ti基非晶的加工區(qū)域尺寸約為20 μm[19] 上述組織分析已給出Mo5中第二相的平均尺寸約為15 μm，體積含量約為20%，由λ = dππ/6f3 (d為平均尺寸，f為體積含量，λ為平均間距)[20]，可計(jì)算出Mo5中β-Ti相的平均相間距約為21 μm 可以看出，Mo5中第二相的尺寸與相間距與基體的加工區(qū)域尺寸十分接近，表明Mo5中第二相與基體間的交互作用增強(qiáng)，更能提高剪切帶的穩(wěn)定性，抑制剪切帶向裂紋的失穩(wěn)轉(zhuǎn)變，提高材料的綜合力學(xué)性能

圖5



圖5不同Mo含量Ti基非晶復(fù)合材料的壓縮斷口及其側(cè)面SEM圖像

Fig.5Compression fractures of the samples with different Mo contents and their lateral SEM images (a, b) Mo0; (c, d) Mo5

析出β-Ti相除了使室溫塑性顯著提高，還使Mo2、Mo5發(fā)生明顯的加工硬化，表1列出了其加工硬化指數(shù) 由表1可見(jiàn)，隨著β-Ti相析出量的增多復(fù)合材料的加工硬化指數(shù)逐漸增大 純非晶合金中局域剪切帶的溫升使其在變形過(guò)程中發(fā)生加工軟化(如圖4中的曲線Mo1所示)，不利于其實(shí)際應(yīng)用，與其相比，非晶復(fù)合材料中析出晶化相的變形使其發(fā)生硬化現(xiàn)象

3 結(jié)論

(1) Mo元素添加量(原子分?jǐn)?shù))較低(≤ 1%)的Ti40Zr10Cu36Pd14非晶合金，仍為純非晶合金；在Mo元素添加量≥ 2%的合金中析出均勻分散的細(xì)小原位β-Ti相，成為原位塑性β-Ti相增強(qiáng)的Ti基非晶復(fù)合材料

(2) 隨著Mo含量的提高β-Ti相的體積分?jǐn)?shù)提高和平均尺寸增大，得到的復(fù)合材料的模量逐漸降低，強(qiáng)度和塑性提高

(3) 在復(fù)合材料的變形過(guò)程中塑性β-Ti相能阻礙剪切帶的快速擴(kuò)展，使剪切帶發(fā)生增殖和偏轉(zhuǎn)，生成多重剪切帶，提高了材料的室溫塑性；同時(shí)，β-Ti相的平均尺寸和相間距與基體的加工區(qū)域尺寸匹配，增強(qiáng)了第二相與基體間的交互作用，提高了剪切帶的穩(wěn)定性 在復(fù)合材料的變形過(guò)程中作為塑性相的β-Ti發(fā)生形變使其發(fā)生明顯的加工硬化

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[J]. Scr. Mater., 2011, 65(6): 532

[12]

Kolodziejska J A, Kozachkov H, Kranjc K, et al.

Towards an understanding of tensile deformation in Ti-based bulk metallic glass matrix composites with BCC dendrites

[J]. Sci. Rep., 2016, 6(1): 22563

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Metallic glass-reinforced metal matrix composites are an emerging class of composite materials. The metallic nature and the high mechanical strength of the reinforcing phase offers unique possibilities for improving the engineering performance of composites. Understanding the structure at the amorphous/crystalline interfaces and the deformation behavior of these composites is of vital importance for their further development and potential application. In the present work, Zr-based metallic glass fibers have been introduced in Al7075 alloy (Al-Zn-Mg-Cu) matrices using spark plasma sintering (SPS) producing composites with low porosity. The addition of metallic glass reinforcements in the Al-based matrix significantly improves the mechanical behavior of the composites in compression. High-resolution TEM observations at the interface reveal the formation of a thin interdiffusion layer able to provide good bonding between the reinforcing phase and the Al-based matrix. The deformation behavior of the composites was studied, indicating that local plastic deformation occurred in the matrix near the glassy reinforcements followed by the initiation and propagation of cracks mainly through the matrix. The reinforcing phase is seen to inhibit the plastic deformation and retard the crack propagation. The findings offer new insights into the mechanical behavior of metal matrix composites reinforced with metallic glasses.

Progress and prospect of solidification research for metallic materials

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2019