冷-热处理对Zr基块体非晶合金结构和性能的影响

传统晶态材料构件或装备在低温环境中会出现可动部分卡死、龟裂、特性改变甚至脆性断裂等现象。低温极端条件如温度突变、高应变速率冲击等对材料性能带来的不利影响严重制约了其在低温极端环境领域的应用。块体非晶合金在低温条件下具有强度更高塑性更好的特殊性能,在极地科考以及航空航天等极端条件下具有极大的应用优势。本文以(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)₉₇Tm₃块体非晶合金为研究对象,研究冷-热处理时间对块体非晶合金的结构、力学性能和腐蚀性能的影响。结果表明,当处理时间由30 min延长到90 min时,试样的晶化体积分数从2.3%增加到4.0%,屈服强度由1701 MPa增加到1810 MPa。在3.5 wt.% NaCl溶液中,合金具有较小的自腐蚀电流密度与较大的电化学阻抗,这意味着经冷-热处理后的块体非晶合金具有优异的耐腐蚀性能。本研究为块体非晶合金在低温极端环境领域的应用提供了强有力的理论支撑。     

不锈钢网增强锆基非晶复合材料的压铸制备及力学性能研究

全程真空压铸技术的快速发展为大块非晶合金的工业化应用提供了可能,受到了广泛关注。但是,非晶合金的室温脆性限制了压铸结构件在一些关键领域的应用。本论文利用压铸工艺高速充型及高压凝固的特性,通过在Vit1锆基非晶合金中引入304不锈钢网叠层焊接制造的骨架,成功制备出了不同体积分数晶态相增强的非晶复合材料,并系统研究了不锈钢网体积分数对力学性能的影响。研究结果表明,不锈钢网在非晶基体中均匀分布,与非晶合金存在冶金界面结合。力学性能测试显示,随着不锈钢编织网的引入,室温脆性的压铸Vit1块体金属玻璃的塑性得到了显著提升。随着不锈钢网目数增大(对应晶态相体积分数增大),非晶复合材料的塑性呈增大的趋势,但是,当目数超过200时,过细的孔洞会导致骨架局部区域无法填充,恶化性能。当晶态相的体积分数为53.7％时,断裂应变达到最大值,约为10％左右,其值高于传统不锈钢纤维增韧的Zr基非晶复合材料。韧化机制分析表明,压铸非晶合金出现脆-延性转变的根本原因是不锈钢网对剪切带扩展进行高效抑制,促进剪切带的增殖和萌生,减少宏观塑性变形的局域化。本研究为非晶复合材料的结构设计提供了新的思路,对于促进非晶合金的更广泛应用具有重要的工程价值。     

Micro-forming characteristics of a Zr-based amorphous alloy with a gear-like mold

The amorphous alloy Zr₆₂Cu₁₇Ni₁₃Al₈ exhibits a supercooled liquid state over a wide temperature range under high temperatures. In this present paper, the authors studied the micro-forming ability of the alloy by compressing specimens under a miniature pattern mold with a micro-gear shape. Micro-compressive formation is a formation method in which the surface of specimens of the Zr₆₂Cu₁₇Ni₁₃Al₈ amorphous alloy is compressed under conditions of dead loads and high temperatures and maintained for a given period for the fabrication of miniature patterns with a micro-gear shape. All the experiments were carried out under a vacuum environment to prevent the specimens from suffering deleterious effects, such as air traps in the miniature patterns and oxidation at the surface of the Zr₆₂Cu₁₇Ni₁₃Al₈ amorphous alloy. The characteristics of micro-compressive formation were investigated at temperatures higher than the glass transition temperature with different experimental parameters of loads and times. In addition, the micro-forming characteristics of the gear-like shape were investigated by means of scanning electron microscopes and a 3-D surface profiler system.     

Elastic moduli and mechanical properties of bulk metallic glasses after quasi-static compression

The effect of quasi-static compressive stress on the elastic moduli and mechanical properties of a Cu₄₆Zr₄₆Al₈ bulk metallic glass (BMG) was investigated. When the applied quasi-static stress is below 2 GPa (equivalent to 1.4 times the yield strength of the BMG), the elastic moduli of the deformed BMGs are found to decrease with the applied stress, revealing the softening or dilatation of the bulk metallic glass. The Poisson ratio is relatively stable when the stress is below 1000 MPa, but it decreases significantly afterwards. Both the plasticity and strength of the BMG are found to increase at low applied stress, and achieve a maximum value before decreasing at higher applied stress. The applied stress is shown to enhance the mechanical properties of the BMG and the properties can be controlled by quasi-static compressive stress. The results demonstrate that an applied stress far below the macroscopic yield strength can still result in microscopic yielding and microstructure change in metallic glass systems.     

Chip formation, cutting forces, and tool wear in turning of Zr-based bulk metallic glass

The chip light emission and morphology, cutting forces, surface roughness, and tool wear in turning of Zr-based bulk metallic glass (BMG) material are investigated. Machining results are compared with those of aluminum 6061-T6 and AISI 304 stainless steel under the same cutting conditions. This study demonstrates that the high cutting speeds and tools with low thermal conductivity and rake angle activate the light emission and chip oxidation in BMG machining. For the BMG chip without light emission, serrated chip formation with adiabatic shear band and void formation is observed. The cutting force analysis further correlates the chip oxidation and specific cutting energy and shows the significant reduction of cutting forces for machining BMG at high cutting speeds. The machined surface of BMG has better surface roughness than that of the other two work materials. Some tool wear features, including the welding of chip to the tool tip and chipping of the polycrystalline cubic boron nitride (PCBN) tool edge, are reported for turning of BMG. This study concludes that BMG can be machined with good surface roughness using conventional cutting tools.     

Preparation, thermal stability, and magnetic properties of Fe---Co---Zr---Mo---W---B bulk metallic glass

A bulk metallic glass (BMG) cylinder of Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a diameter of 1.5 mm was prepared by copper mould casting of industrial raw materials. The amorphous state and the crystallization behavior were investigated by X-ray diffraction (XRD). The thermal stability parameters, such as glass transition temperature (T_g), crystallization temperature (T_x), supercooled liquid region (ΔT_x) between T_g and T_x, and reduced glass transition temperature T_rg (T_g/T_m) were measured by differential scanning calorimetry (DSC) to be 891, 950, 59 K, and 0.62, respectively. The crystallization process took place through a single stage, and involved crystallization of the phases -Fe, ZrFe₂, Fe₃B, MoB₂, Mo₂FeB₂, and an unknown phase, as determined by X-ray analysis of the sample annealed for 1.5 ks at 1023 K, 50 K above the DSC peak temperature of crystallization. Mössbauer spectroscopy was studied for this alloy. The spectra exhibit a broadened and asymmetric doublet-like structure that indicated paramagnetic behavior and a fully amorphous structure. -Fe was found in the amorphous matrix for a cylinder with a diameter of 2.5 mm. The success of synthesis of the Fe-based bulk metallic glass from industrial materials is important for the future progress in research and practical application of new bulk metallic glasses.     

Mo microalloying effect on the glass-forming ability, magnetic, mechanical and corrosion properties of (Fe0.76Si0.096B0.084P0.06)100-xMox bulk glassy alloys

The effect of Mo addition on the glass-forming ability (GFA), magnetic properties, mechanical properties and corrosion resistance of (Fe_0.76Si_0.096B_0.084P_0.06)_100−xMo_x (x = 0, 2, 4 and 6 at.%) bulk glassy alloys (BGAs) with high Fe contents was investigated. The 2 at.% Mo addition makes the alloy composition approach towards a eutectic point, which could result in an increase in the GFA. The BGA rod with diameters up to 3.5 mm was produced by copper mold casting. These BGAs exhibit a rather high saturation magnetization of 0.98-1.51 T and lower coercive force of 1.7-2.1 A/m. A significant improvement in corrosion resistance was observed with microalloying Mo element in 1 N H₂SO₄ solution. Furthermore, these Fe-based BGAs show super-high strength of ∼3.3 GPa and Young's modulus of 200 GPa.     

Thermal stability and mechanical properties of Gd-Co-A1 bulk glass alloys

The glass forming ability of Gd-Co-A1 ternary alloy systems with a composition ranging from 50% to 70% （molar fraction） for Gd and from 5% to 40% （molar fraction） for AI were investigated by copper mold casting and Gd60Co25Al15 bulk glass alloy cylinders with the maximum diameter of 5 mm were obtained. The reduced glass transformation temperature （TG/Tm） and the distance of supercooling region ATx are 0.616 and 45 K, respectively for this Gd-Co-A1 alloy. The compressive fracture strength （σf） and elastic modulus （E） of Gd-Co-A1 glassy alloys are 1 170-1 380 MPa and 59-70 GPa, respectively. The Gd-AI-Co bulk glassy alloys with high glass forming ability and good mechanical properties are promising for the future development as a new type function materials.     

Wear and thermal properties of Zr-based amorphous surface alloyed materials fabricated by high-energy electron beam irradiation

Zr-based amorphous surface alloyed materials were fabricated by high-energy electron beam irradiation in this study. A mixture of Zr-based amorphous powders and LiF + MgF₂ flux was deposited on a pure copper substrate, and then an electron beam was directed on this powder mixture to fabricate a one-layered surface alloyed material. A two-layered surface alloyed material was also fabricated by irradiating electron beam again onto the powder mixture deposited on the one-layered surface alloyed material. The microstructural analysis results indicated that a number of coarse crystalline phase particles were formed in the one-layered surface alloyed layer, whereas a small amount of fine and hard crystalline particles were homogeneously distributed in the amorphous matrix of the two-layered surface alloyed layer. Owing to these fine and hard crystalline particles, the hardness and wear resistance of the two-layered surface alloyed layer improved over the one-layered surface alloyed layer or other kinds of surface alloyed layers. The thermal conductivity of the two-layered surface alloyed layer was much lower than that of titanium-alloy-based or stainless-steel-based surface alloyed layers. These findings suggested the possibility of applying Zr-based amorphous surface alloyed materials to high wear-resistant thermal barrier coatings or parts.     

挤压速度对双通道等径角挤压7003铝合金力学性能的影响

采用扫描电镜、显微硬度计及万能试验机研究了挤压速度对双通道等径角挤压对7003铝合金力学性能的影响。结果表明：在任一挤压速度下,随着挤压道次的增加,材料的力学性能明显改善;挤压一道次后试样的抗拉强度由338.3 MPa提高到384.5 MPa,二道次后提高到431.5 MPa;屈服强度经一道次挤压后由260 MPa提高到325 MPa,二道次后提高到426 MPa,二道次涨幅更明显;随着挤压速度的增大,试样断后伸长率的变化总体上均呈现下降的趋势,当挤压速度为25 mm/min 时,一道次挤压后伸长率最小;经二道次挤压后的显微硬度,在挤压速度为25 mm/min时由原样退火态的73.5 HV提高到136.4 HV,且强度以及显微硬度均在挤压速度为25～35 mm/min时达到了最大值。     

等通道球形转角膨胀挤压工业纯铝的组织与性能

采用新型等通道球形转角膨胀挤压(equal channel angular expansion extrusion with spherical cavity,ECAEE-SC)工艺,对工业纯铝进行室温1道次挤压变形。借助光学显微镜(OM)、电子背散射衍射(EBSD)研究变形过程中工业纯铝显微组织的变化规律,并进行了硬度测试和拉伸试验。结果表明:ECAEE-SC工艺具有复合成形效果和较高的挤压效率,坯料成功实现了单道次连续变形。工业纯铝经1道次ECAEE-SC变形后,在机械剪切、应变累积和静水压力的共同作用下,晶粒显著破碎和细化,内部形成了大量细小、均匀的等轴亚晶,平均晶粒尺寸约为4.6mm;材料表现出优良的综合力学性能,HV显微硬度由未变形时的366 MPa增加至702 MPa,增幅为91.8%,且分布趋于均匀;抗拉强度高达183.8 MPa,而伸长率降低至12.7%,拉伸断口表现出明显的韧性断裂特征。     

等径角轧制AZ31镁合金板材的组织与性能

采用等径角轧制工艺制备了AZ31镁合金板材.结果表明:经等径角轧制后的板材,晶粒取向由等径角轧制前的(0002)基面取向演化为基面与非基面共存的取向.与等径角轧制前的板材相比,板材晶粒尺寸略有长大并有孪晶出现,但强度却明显提高,而断裂延伸率变化不大,尤其是1个道次轧制的板材其抗拉强度由等径角轧制前的240增大到275 MPa,屈服强度由193.8增大到239.2 MPa;随着等径角轧制道次的增加,板材的强度逐渐降低,至第4个道次其抗拉强度仅为250 MPa,屈服强度为207.3 MPa.     

Microstructure and mechanical properties of ultrafine grained Mg97Y2Zn1 alloy processed by equal channel angular pressing

The Mg₉₇Y₂Zn₁ alloy processed by equal channel angular pressing (ECAP) has been investigated. It was found that the blocks of secondary phase were broken into uniform distributed sections after ECAP. The Mg₉₇Y₂Zn₁ alloy processed by ECAP obtained ultrafine grains and exhibits excellent mechanical properties. The average grain size of about 330 nm, yield strength (YS) of 400.3 MPa and ultimate tensile strength (UTS) of 450.0 MPa were obtained by two-step ECAP of 4 passes at 623 K and 2 passes at 603 K. The long-period stacking (LPS) structures contribute to the formation of ultrafine grains in ECAP processed Mg₉₇Y₂Zn₁ alloy. The results demonstrate that ECAP instead of rapid solidified powder metallurgy (RS/PM) can refine grain size and enhance the strength of Mg₉₇Y₂Zn₁ alloy. It was also found that the elongation of alloy is decreased with increasing pass number. It was found that cracks were preferentially initiated and propagated in the interior of X-phase during the process of ECAP.     

Effects of rare-earth elements on the glass-forming ability and mechanical properties of Cu46Zr47-xAl7Mx (M = Ce, Pr, Tb, and Gd) bulk metallic glasses

Cu46Zr47-xAl7Mx(M = Ce,Pr,Tb,and Gd) bulk metallic glassy(BMG) alloys were prepared by copper-mold vacuum suction casting.The effects of rare-earth elements on the glass-forming ability(GFA),thermal stability,and mechanical properties of Cu46Zr47-xAl7Mx were investigated.The GFA of Cu46Zr47-xAl7Mx(M = Ce,Pr) alloys is dependent on the content of Ce and Pr,and the optimal content is 4.at %.Cu46Zr47-xAl7Tbx(x = 2,4,and 5) amorphous alloys with a diameter of 5 mm can be prepared.The GFA of Cu46Zr47-xAl7Gdx(x = 2,4,and 5) increases with increasing Gd.Tx and Tp of all decrease.Tg is dependent on the rare-earth element and its content.△Tx for most of these alloys decreases except the Cu46Zr42Al7Gd5 alloy.The activation energies △Eg,△Ex,and △Ep for the Cu46Zr42Al7Gd5 BMG alloy with Kissinger equations are 340.7,211.3,and 211.3 kJ/mol,respectively.These values with Ozawa equations are 334.8,210.3,and 210.3 kJ/mol,respectively.The Cu46Zr45Al7Tb2 alloy presents the highest microhardness,Hv 590,while the Cu46Zr43Al7Pr4 alloy presents the least,Hv 479.The compressive strength(σc.f.) of the Cu46Zr43Al7Gd4 BMG alloy is higher than that of the Cu46Zr43Al7Tb4 BMG alloy.