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Ti-Zr-V-Cu-Be BMGMCs processed by semi-solid processing

Hong-Min Guo1, a,*, Le-Rong Bai2,b, Bin Liu2,c, Xiang-Jie Yang3

1 School of Materials Science and Engineering, Nanchang University, Nanchang, P.R. China

2School of Materials Science and Engineering, Nanchang University, Nanchang, P.R. China
3School of Materials Science and Engineering, Nanchang University, Nanchang, P.R. China
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Abstract

A series of in situ two-phase bulk metallicglassmatrixcomposites (BMGMCs) have beendeveloped, which exhibitimproved toughness, compared to the monolithic bulk-metallicglassesat room temperature. However, most of the plastic in situ BMGMCs aredeveloped through extremely rapid cooling, during which thesolidification process cannot be controlled effectively. As a consequence, the microstructures of in situ two-phase compositeseven with the same composition vary from one to another,highly dependent on the cooling rate.

In the present investigation, the Ti-Zr-V-Cu-Be BMGMCs was prepared by using copper mould suction process, the evolution of microstructure of this kind of Ti based BMGMCs at semi-solid stage was investigated. The results indicated that microstructures of billets, produced by copper mould suction and water quenching after isothermal holding at semi-solid stage, mainly contained β-Ti phase and glass matrix. Isothermal holding temperature and time interval determined the final morphology of β-Ti phase. Compression tests showed that semi-solid processing was effectiveto obtain BMGMCs with further improved ductility.

Keywords:bulk metallic glass composites (BMGCs);microstructure; semi-solidprocessing

  1. introduction

In recent years,bulk metallic glasses are numerously studied profit by their excellent properties such aslargelimit of elasticity, high strength, and attractivecorrosionresistance[1]. But problems appear when it used to be practical structural applications for their limited plasticstrain, which occurs to brittle-fracturebehaviour when under deformation. The reason of this behaviour was considered as the propagation of highly localized shear bands, thus leading to led tocatastrophic failure. As a result, plentiful researches wereimplemented hammering at improving the toughness and ductility[2-6]. It was reported that superiormicrostructure in Ti-based bulk metallic glasses can lead the transformation from localized shear bands to multiple shear bands, thus bring to a longer hours deformation and improved global plasticstrain [3,4]. Furthermore, it was identified that Ti-based bulk metallic glasses after semi-solid processing could achieve it.The presentauthors reporteda method to change the morphology, size and volume fraction of the original amorphous alloy phase by choosing the proper holding temperature and time in semi-solid processing. So that the purpose of this studies to analyze the mechanical propertiesof Ti-based bulk metallic glassesin various crystal tissues after semi-solid isothermal heat treatment, and ultimately, obtain the best controlling scheme of enhancing mechanical properties.[7]

  1. Experimental

Ingots with a composition ofT42Zr22V14Cu5Be17 (at %) and Ti46Zr20V12Cu5Be17 (at%) (in the following passage which would be called T42 and T46) mixtures of Ti, Zr, V, Cu and Be with no less than 99.99% purityin a Ti-gettered argon atmosphere, next the metals would be melted 3-5 times with the magnetic stirrerturning on to ensure to obtain the chemical homogeneity before it sucked into a water-cooledcopper mold, and the ultimate aim is to get a series of bulk metallic glass composite rods with 70mm in length and 4 mm in diameter. The rods with 20 g were cut into a lot of parts with proper length for quartz tube vacuum capsulation, followed by semi-solid isothermal heat-treatment.

The microstructure of semi-solid isothermal treatment samples after polishing and etching in the solution of 2% Hcl, 2% HF, 1% HNO3 and 95%distilledwater for 10-15 s was analyzed by scanningelectron microscopy (SEM; Quanta FEG), and it was investigated by X-ray diffraction (XRD)with the CuKa radiation. Table 1 shows the selection of temperature and time for semi-solid isothermal heat treatment.

Table 1.The selection of temperature and time for semi-solid isothermal heat treatment.

Alloy composition

/ Thermal insulation temperature of semi - solid isothermal treatment for 10min.（）
T42 / 800 / 860 / 900

Alloy composition

/ Thermal insulation temperature of semi - solid isothermal treatment for 20min.（）
T46 / 800 / 860 / 900

The thermal properties analysis was tested by the differentialscanningcalorimetry (DSC) at the heating rate of 20K/min. The mechanical properties were presented by uniaxial compressive test, which used a universal mechanical tester with the loading rate of 1×10-4s-1

  1. Results and discussion

3.1. Microstructure, XRD patterns and. Thermal properties. Fig.1 shows the microstructure which was composed by amorphous matrix and the same kind of dendritic crystal (wesay it the second phase) after 10min of isothermal heat treatment at different temperatures of T42amorphous composite. It can be seen from Fig.1 that its microstructure has obvious changes with the variation of temperature in thesame thermalinsulationtime. When the temperature held at 800, as Fig.1 (b) shows, the dendritic tissues begin to break down, and the small dendritic arms disappear into irregular shape, in which there are obviouschanges between the as-cast state structure and the latter. For (c), when the temperature rose to 860, sphericity of the second phase could be observed. But when the temperature climb to 900 , shown in (d), there is a tendency to grow up of the crystal phase with the sphericity going to bad somewhat, and this can be an evidence that the sphericity of the crystal could be destructed and the small spherical crystal tend to converge as the holding temperature increased to 900 .

Fig.3 demonstrates the XRD and DSC curves ofT42 andT46 amorphous composite after semi-solid isothermal treatment for 10 min. According to the Fig.3 (a) the structure of thecrystalline phase was not altered somewhere by semi-solid processing, and the sharp peak is still corresponded to the monocrystallineβ-Ti through the comparison with PDF card.

Fig.1.The metallographic microstructure of T42 amorphous composite at different temperatures with the semi-solid isothermal heat treatmentfor10 minutes.(a) As-cast; (b) 800; (c) 860; (d) 900.

(a) (b)

Fig.3 (a) XRD and (b) DSC curves of Ti42 and Ti46 after semisolid processing

3.2. Mechanical properties. Fig.4 reveals the compression engineering stress-strain curves of the T42 and T46amorphous composite before and after semi-solid processing. In picture (b) the curves were divided to a, b and c respectively according to different holding temperature and holding time in the processing.

Table 2 shows the ultimate strength (u) and the plastic strain(u) of T42 and T46amorphous composite in solid and after semi-solid processing. It is shown that before the semi-solid processing, on the one side the T42 alloy exhibits the ultimate strength of 1915MPa with the plastic strain of 13.1%, and on the other side, the T46 alloy get 1854MPa and 14.1% in the ultimate strength and plastic strain respectively. After holding the time and temperature at 10 min, 860 , T42 alloy shows a ultimate strength of 2101MPa following by a plastic strain of 18.2%, in which T46 alloy get the 2079MPa and 24.1%, and it means there are obviously promotion in ultimate strength and plasticity of T42 and T46amorphous composite after semi-solid processing. But when the holding time increased to 20 min, something bad occurs to T42 alloy, for it only obtain 1501MPa and 17.1% in ultimate strength and plastic strain individually. But even in this case, the T42 alloy also get the higher plasticity than in the as cast state. It can be illustrated by the data above that the plasticity and ultimate strength of Ti-based amorphous composite could be obviously improved by implementing proper holding temperature and holding time in semi-solid processing.

(a) (b)

Fig.4 the compression engineering stress-strain curves of the T42 and T46 alloys.(a) As-cast; (b) Semi-solid processing.

Table 2.Mechanicalproperties of T42 and T46 alloys before and after semi-solid processing.

Alloy composition

/ As-cast / semi-solid processing of 860, 10min / semi-solid processing of 860, 20min
T42 / 1915MPa / 13.1% / 2101MPa / 18.2% / 1501MPa / 17.1%
T46 / 1854MPa / 14.1% / 2076MPa / 24.1% / - / -
Mechanicalproperties / u / u / u / u / u / u
  1. Conclusions

1)There are obvious changes of T42 and T46 amorphous composite after semi-solid processing at different holding temperature for 10 min. With the increasing of holding temperature, the dendritic phase begins to decompose and fuse, also we can see the shape factorincrease at the early stage and then decrease.

2)Neither the holding time nor the holding temperature could change the crystal phase structure, and the sharp peak in XRD spectrum still corresponded to the bbc β-Ti.

3)When de holding temperature and holding time in semi-solid processing are controlled in 860 and 10min individually, we can get the best mechanical properties, in which on the one hand the T42 alloy exhibits the ultimate strength of 2101MPa with the plastic strain of 18.2%, and on the other hand, the T46 alloy get 2076MPa and 24.1% in the ultimate strength and plastic strain respectively.

  1. References

[1] Inoue A. Bulk Amorphous AlloysMater. Rev., 1999, 43(6):365-520.

[2]Terajima T, Nakata K, Kimura H, et al. Development of W-Reinforced Zr-Based Metallic Glass. Journal of the Japan Institute of Metals, 2009, 50(6):1322-1325.

[3] He G, Eckert J, Löser W, et al. Novel Ti-base nanostructure-dendrite composite with enhanced plasticity. Nature Materials, 2003, 2(1):33-37.

[4] Hofmann D C, Suh J Y, Wiest A, et al. Designing metallic glass matrix composites with high toughness and tensile ductility. Nature, 2008, 451(7182):1085-1089.

[5] Eckert J, Kühn U, Mattern N, et al. Structural bulk metallic glasses with different length-scale of constituent phases. Intermetallics, 2002, 10(11–12):1183-1190.

[6] Kuhn U, Eckert J, Mattern N, et al. ZrNbCuNiAl bulk metallic glass matrix composites containing dendritic bcc phase precipitates. Applied Physics Letters, 2002, 80(14):2478-2480.

[7]T. Zhang, H.Y. Ye, J.Y. Shi, H.J. Yang, J.W. Qiao, Dendrite size dependence of tensile plasticity of in situ Ti-based metallic glass matrix composites, J. Alloy.Compd. 583 (2014) 593-597.

15th International Conference on Semi-Solid Processing of Alloys and Composites

October 22nd-24th, 2018, Shenzhen, China