Liquidus Temperature Tl Research Articles

New criterion of glass forming ability for bulk metallic glasses

It has been confirmed that glass-forming ability (GFA) is related to not only liquid phase stability but also the crystallization resistance. In this study, it was found the liquidus temperature Tl and supercooled liquid region Tx−Tg could reflect the stability of glass-forming liquids at the equilibrium and undercooled state, respectively, while the onset crystallization temperature Tx could indicate the crystallization resistance during glass formation. Thus, a modified γ parameter, defined as γm=(2Tx-Tg)∕Tl, has been established. This parameter shows an excellent correlation with the GFA of bulk metallic glasses, with the statistical correlation factor of R2=0.931.

Glass Forming and Thermal Properties of the Mg<sub>65</sub>Cu<sub>25</sub>GD<sub>10-x</sub>Nd<sub>x</sub> (x=0~10) Amorphous Alloys

The Mg65Cu25Gd10-xNdx (x=0 ~ 10) amorphous alloy rods with 3~6 mm in diameter were prepared by Cu-mold injection method. The thermal properties and mechanical properties of these amorphous alloys have been investigated by DSC, SEM with EDS capability, X-ray diffractometry (XRD) and Vickers hardness test. The XRD revealed that these entire as-quenched Mg65Cu25Gd10-xNdx alloy rods exhibit a broaden diffraction pattern of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 30~60 K) were revealed for all of those Mg65Cu25Gd10-xNdx alloys. In addition, the single stage crystallization of the Mg65Cu25Gd10 alloy was found to change into two stages crystallization when the Nd element was added into this alloy. In parallel, the crystallization temperature (Tx) and supercooled region (Tx) presents a decreasing trend with increasing Nd content. The lowest liquidus temperature (Tl, about 721 K) occurs at the Mg65Cu25Gd8Nd2 alloy. In addition, The Mg65Cu25Gd8Nd2 alloy exhibits the high γ value (0.416, defined as γ= Tx/Tg+Tl), a relatively high Trg (0.59, defined as Trg = Tg/Tl) and the highest hardness in these alloys.

Glass forming ability criteria for La–Al–(Cu, Ni) alloys

Criteria for evaluating the glass forming ability (GFA) of La–Al–(Cu,Ni) alloys were studied. The GFA criteria can be categorized into two types, according to whether the liquidus temperature Tl is included in the formula or not. The Tl inclusive criteria generally predict a maximum in GFA at the eutectic composition at which Tl is a minimum. However, for La–Al–(Cu,Ni) alloys, the best GFA does not correspond to the eutectic. The paper discusses the suggestion that the solidification temperature Ts should be used instead of Tl for evaluating the GFA of La–Al–(Cu,Ni) alloys.

Superior glass-forming ability of CuZr alloys from minor additions

We report a novel phenomenon in which minor element additions (∼1 at.%) can dramatically enhance the glass-forming ability (GFA) of CuZr(Al) metallic alloy, which can be cast into glasses with large cross-section sizes using a conventional casting method. The minor additions cause the liquidus temperature Tl to decrease from 1219 (for Cu50Zr50) to 1139 K [for (Cu50Zr50)92Al7Gd1], and the reduced glass transition temperature Trg (=Tg/Tl) of the alloys increases from 0.550 (for Cu50Zr50) to 0.613 [for (Cu50Zr50)92Al7Gd1]. The mechanism involved in the achievement of the superior GFA is explained by the stronger tendency of short-range ordering in the stronger microalloyed alloys as well as the thermodynamic and kinetic aspects.

Effects of Additional Hf on the Thermal Stability and Mechanical Properties of Cu-Zr-Ag Bulk Glassy Alloys

The thermal stability, crystallization behavior and mechanical properties of the Cu45Zr45� xHfxAg10 (x ¼ 0 to 45 at%) glassy alloys have been investigated. The glass transition temperature (Tg), crystallization temperature (Tx), liquidus temperature (Tl) and the supercooled liquid regionTx (¼ TxTg) increase with increasing Hf content. The reduced glass transition temperature (Tg=Tl) values are in the range from 0.54 to 0.59. The Vicker's hardness (HV ), Young's modulus (E) and compressive fracture strength (� c,f) of the Cu45Zr45� xHfxAg10 (x ¼ 0 to 25 at%) bulk glassy alloys increase linearly with increasing Hf content and reach the maximum values of 554, 123 GPa and 2020 MPa, respectively, for Cu45Zr20Hf25Ag10 alloy. A different crystallization behavior is observed for Cu45Zr45Ag10 and Cu45Hf45Ag10 glassy alloys. (doi:10.2320/matertrans.47.1922) the thermal stability and mechanical properties of Cu-based Cu-Zr-Ag bulk glassy alloys. This paper presents the thermal stability, density and mechanical properties of the Cu-Zr-Hf- Ag glassy alloys. The effectiveness of substitution of Hf for Zr is also investigated. 2. Experimental Procedure Multi-component Cu-(Zr, Hf)-Ag alloy ingots with nom- inal compositions were prepared from the mixtures of pure Cu, Zr, Hf and Ag metals by arc melting in a Ti-gettered argon atmosphere. The purity of metals was over 99.9 mass%. Alloy ingots were re-melted four times to ensure chemical homogeneity. The glassy alloys in a ribbon form with a cross section of 0:02 � 1:5 mm 2 and in a cylindrical rod form with diameters up to 2.0 mm were prepared by melt spinning and copper mold casting, respectively. The glassy structure was identified by X-ray diffraction and the thermal stability associated with glass transition temperature (Tg) and crystallization temperature (Tx) was examined by differential scanning calorimetry (DSC) at a heating rate of 0.67 K/s. The liquidus temperature (Tl) was measured by differential thermal analyzer (DTA) at a heating rate of 0.33 K/s. The density was measured by Archimedes's principle by weigh- ing ingots in tetrabromoethane and in air. Vicker's hardness was measured using a microhardness tester. Mechanical properties were measured under a compressive load with an Instron testing machine. The gauge dimension of specimens was 2.0 mm in diameter and 4.0 mm in height and the strain rate was 5 � 10 � 4 s � 1 .

Evaluation on the reliability of criterions for glass-forming ability of bulk metallic glasses

Evaluation on the reliability of criterions for glass-forming ability of bulk metallic glasses

Fabrication of Bulk Amorphous Mg65Cu25Gd10 Alloy of 12mm Rod by Water Quenching

Bulk armorphous Mg65Cu25Gd10 alloy of 12mm rods were prepared by water quenching the molten alloy in the stainless steel tube. Neither cavities nor voids are seen over the whole range and no contrast revealing a crystalline phase is seen over the transverse cross section. The glass transition temperature (Tg), crystallization temperature (Tx), the melting temperature (Tm) and the liquidus temperature (Tl) are measured to be 419K, 492K, 702K, 735K, respectively, for the Mg65Cu25Gd10 alloy with a diameter of 12mm. These temperatures are similar with those of the alloy with a diameter of 8mm produced by metallic mould casting. Both alloys have the same Vickers hardness about 260. Water quenching can further improve the critical diameter of glassy rods, so it is qualified for the formation of the bulk alloys.

New Ti-Based Bulk Glassy Alloys with High Glass-Forming Ability and Superior Mechanical Properties

Ti-based glassy alloy rods with diameters up to 5 mm were prepared for Ti41.5Zr2.5Hf5Cu42.5Ni7.5Si1 in a multi-component system of (Ti, Zr, Hf)-(Cu, Ni)-Si by conventional copper mold casting. The new mutli-component glassy alloy exhibits moderate thermal stability with a supercooled liquid region (ΔTx) above 50 K. The glass transition temperature (Tg), crystallization temperature (Tx), melting temperature (Tx), liquidus temperature (Tl), and the reduced glass transition temperature (Tg/Tl) are 680 K, 730 K, 1143 K, 1199 K and 0.57, respectively. The cast glassy alloy exhibits compressive strength of 2080 MPa, tensile strength of 2040 MPa and Young's modulus of 100 GPa. The reason for the high glass-forming ability (GFA) of the Ti-based multi-component alloy is discussed on the basis of knowledge available for bulk glass formation.

Thermal Stability and Mechanical Strength of Bulk Glassy Ni-Nb-Ti-Zr Alloys

Bulk glassy Ni-based alloys with high fracture strength exceeding 2700 MPa were prepared in Ni60Nb40−x−yTix Zry system by copper mold casting. The glassy alloys with distinct glass transition were obtained in the wide composition range from 0 to 35%Ti and 0 to 30%Zr and the largest supercooled liquid region before crystallization was 76 K for Ni60Nb15Ti10Zr15. The maximum diameter was 2 mm for Ni60Nb20Ti15Zr5 and the glass transition temperature (Tg), crystallization temperature (Tx) and reduced glass transition temperature (Tg/Tl) of the bulk glassy alloy were 841 K, 898 K and 0.61, respectively. The Young’s modulus (E), compressive fracture strength (σc,f) and compressive fracture elongation (ec,f) were 156 GPa, 2770 MPa and 2.4%, respectively, for the bulk alloy. There is a tendency for fracture strength to increase with increasing E , Tg and liquidus temperature (Tl). It is therefore interpreted that the high strength is due to strong bonding nature among the constituent elements.

Effects of BaO on the glass formation of the PbO-B2O3-TiO2-BaO system in relation to transition temperatures

The variation of the BaO content on the quaternary PbO-B2O3-TiO2-BaO system's glass formation tendency was investigated in relation to transition temperatures, such as melt temperature (T f), liquidus temperature (T l), crystallization temperature (T c) and glass transition temperature (T g). Compositions were melted between 800°C and 1300°C. In order to obtain bulk glass samples, glass formation was carried out using a preheated cylindrical brass mould without forcing the cooling rate to increase. Glass formation tendency increased with increasing the temperature ratios of T g/T l and T c/T l and with decreasing T g/T c. Eutectic compositions preferentially formed glasses from melts due to their low melting temperatures.

Studies of the effect of paramagnetic impurity in the structure of sodium disilicate glass

Magic angle spinning nuclear magnetic resonance (MAS NMR) is used to measure the 29Si chemical shift and full width at half maximum in Na2O·2SiO2·xMnO for 0.0≤x≤0.8 glasses. The large space varying magnetic field of the paramagnetic centers increases the line width and moves the chemical shift to a lower frequency, i.e. more shielded, with the increase of Mn++. The T1 relaxation time falls rapidly and the relaxation rate is shown to be proportional with the concentration of MnO. The differential thermal analysis (DTA) results show that the glass transition temperature, Tg, crystallization temperature, Tx, and liquidus temperature TL do not change due to addition of MnO. This suggests that Mn++ does not form chemical bond with the network. However, the Mn++ acts as nucleating agent and enhances the crystallization and the rate of crystallization can be tailored by judicious choice of the amount of MnO.

Formation and Thermal Stability of Gels in the SiO<sub>2</sub>-TiO<sub>2</sub>-ZrO<sub>2</sub> System

Gels were prepared in the SiO2-TiO2-ZrO2 system (SiO2, TiO2 and ZrO2=0-100mol%) from Si(OC2H5)4, Ti(O-isoC3H7)4 and Zr(O-nC3H7)4 solutions with or without H2O and CH3COOH. Without H2O and CH3COOH transparent bulk gels were formed in the range 30-100mol% SiO2, 0-70mol% TiO2 and 0-50mol% ZrO2 and opaque bulk gels in the rest compositions. X-ray diffraction measurement indicated that all the gels were non-crystalline even after drying at 50°C for 3 days. Crystallization peak temperatures Tc were determined by DTA on the dried gels preliminarily heat-treated at 200°C for 1h. Tc was low in the TiO2-ZrO2 rich compositions (Tc=366°C for TiO2 and 419°C for ZrO2). Tc increased up to 1258°C with increasing SiO2 content. From Tc and liquidus temperature TL, Tc/TL ratio was calculated. Tc/TL ratio means the thermal stability of the amorphous solids. It was discovered that TiO2 and ZrO2 alone are thermally unstable (Tc/TL=0.3 for TiO2 and 0.23 for ZrO2) but mixing TiO2 with ZrO2 enhances the thermal stability (for example, Tc/TL=0.45 for 50TiO2⋅50ZrO2) with increased ability of forming amorphous phase (amorphous-forming ability). This is true in the SiO2-TiO2-ZrO2 system for fixed SiO2 concentrations. Tc/TL increased with SiO2 content and reached the highest value of 0.86 at 90SiO2⋅10TiO2 composition, which is higher than that of SiO2 (0.77). Yet it seems likely that there are more stable compositions centering around the 80SiO2⋅10TiO2⋅10ZrO2 in the SiO2-TiO2-ZrO2 system. It is expected that compositions of high Tc/TL value have a high amorphous-forming ability.

Ｂ２Ｏ３‐Ｎａ２Ｏ‐Ａｌ２Ｏ３系のゲルの熱的安定性とガラス化領域

The thermal stability of gels in the B2O3-Na2O-Al2O3 system was evaluated by two methods; (1) observation of the change of amorphous region after heating up to 200-800°C at a heating rate of 1°C/min and keeping for 2h, and (2) determination of the crystallization temperature Tc from the DTA curve of gels with heating rate of 5°C/min and calculation of the ratio of Tc to the liquidus temperature Tl, Tc/Tl. After heating gels up to 800°C, the original gel region, which extends over a wide area including Al2O3, was reduced to only a small amorphous region near the Al2O3 rich area. The Tc/Tl ratio showed the highest value of more than 0.8 in the composition range B2O3=55-90mol% and Al2O3=0-20mol%, while it was less than 0.6 value in the Al2O3 rich composition area. The compositional dependence of Tc/Tl ratio was compared with the variation of the glass-forming region obtained from melt at various cooling rates Q in the range of logQ=-2 to 5. It was recognized that the gel region having a high Tc/Tl value corresponds to a stable glass region obtainable under slow cooling. It seems that some close relationship exists between the Tc/Tl of a gel and the critical cooling rate Q* for glass formation of a melt having the same composition.

Improvement of Workability of Alkali-Resistant BaO-SiO<sub>2</sub>-TiO<sub>2</sub> Glass

In order to improve workability of alkali-resistant BaO-SiO2-TiO2 glasses, glass-forming ability was evaluated for various glass compositions obtained by partial replacement of 30BaO, 30SiO2, 40TiO2 in mol% with Li2O, Na2O, CaO, SrO, Al2O3 and/or ZrO2 (Tables 1-4). Here, a parameter Kgl was employed for estimating glass-forming ability. This was expressed as (Tc-Tg)/(Tl-Tc) by Hruby, where glass transition temperature Tg, crystallization temperatrure Tc and liquidus temperature Tl are determined on the differential thermal analysis curves (Fig. 2). It was found that the composition of 7.0Na2O, 5.75CaO, 5.75SrO, 11.5BaO, 30.0SiO2, 33.0TiO2, 7.0ZrO2 in mol% gives the largest Kgl value among the examined compositions. Melt of this composition could be drawn into a continuous long fiber 8-15μm in diameter and 50, 000m long with a specially designed double-crucible method (Fig. 3). Glass fibers of this composition were confirmed to be alkali-resistant and showed no diameter reduction even after exposure to either Portland cement aqueous phase solution or a 2N NaOH solution at 95°C for 18h.

Calculation of Cp(T) for liquid Li/Pb alloys from experimental ρ(T) and (δp/δT)sdata

The density rho and the adiabatic variation of temperature T with pressure p, ( delta T/ delta p)s, have been measured for the whole concentration range of liquid Li/Pb alloys and for a temperature range of 200 to 700 K (depending on composition) above the liquidus temperature TL. The heat capacity Cp calculated from these data exhibits a pronounced peak at the composition Li4Pb where at TL it exceeds the ideal Cpi by an excess value Cpxs of about 0.8 Cpi. Linear variation of Cp with T was only observed for pure liquid Pb. Strongly bent curves with more or less pronounced minima were observed for the other compositions, including pure liquid Li. The Cpxs of liquid Li4Pb compares well with a value calculated from neutron diffraction data by Ruppersberg and Schirmacher (1984).

Melting of Ni40Pd40P20 glass

Upon reheating, most glassy metal alloys crystallize at a temperature not far removed from the glass temperature Tg and far below the liquidus temperature Tl. We have reported that the alloy Ni40Pd40P20, which exhibits a scaled glass temperature ∼0.68, has been melt quenched, under a flux of dehydrated B2O3, to glass at rates as low as 1°/s. Here we report experiments in which some specimens of this alloy, when similarly fluxed during reheating, have been reheated to temperatures within 50° of Tl and 280° above Tg at rates ∼2.5°/s, and then cooled again to Tg, without crystallization. From this behavior we infer that the steady frequency of homogeneous nucleation of crystals in the alloy is <10−1 cm−3 s−1.

Chemical short-range order in liquid LiPb alloys

The partial structure factor SCC(q) of liquid Li0.8Pb0.2 is determined at five different temperatures between the liquidus temperature TL and (TL+230)K. Its temperature dependence can be described as a simple function of a q-space potential. Combining X-ray and neutron diffraction patterns, approximate curves for SCC(q) and SNN(q) are obtained for Li0.5Pb0.5 and Li0.62Pb0.38.