Microstructure And Tailoring Of Cu-Zr Based Amorphous Alloy Quenching At Low Temperature

As-cast B2-CuZr/CuZr-based amorphous composites are considered one of the amorphous materials with engineering application prospects.The mechanical properties depend on the internal phase composition and the volume fraction and distribution of the B2-CuZr phase.The results of CuZr-based amorphous composites prepared by high temperature suction（spray）casting,semi-solid casting and continuous casting confirm that rapid quenching temperature is an important factor determining the microstructures and properties of amorphous composites.The effects of rapid quenching temperature and constant temperature treatment at low temperature on the microstructures of Cu-Zr-Al amorphous alloy were studied by XRD,OM,SEM,EDS,DSC and compressive performance test.The research results will promote the low temperature copper mold casting technology of B2-CuZr/CuZr-based amorphous composites.Firstly,for the Cu_47.5Zr47.₅Al₅ amorphous alloy,theΦ5mm alloy samples were prepared by water quenching quartz tube at near liquidus temperature（900°C）,above liquidus temperature（930°C）,constant temperature treatment at 930°C and remelting temperature（960°C）.The results show that when the rapid quenching temperature is at near liquidus temperature 900°C,the glass forming ability of the alloy is very weak,and the firstly precipitated phase B2-CuZr is mostly decomposed.The sample is mainly composed of Cu₁₀Zr₇ and CuZr₂.It is difficult to obtain a single B2-CuZr crystal phase by rapid quenching at near liquidus temperature.When the quenching temperature is 960°C and 930°C above the liquidus,the alloy has a certain glass forming ability.With the increase of quenching temperature,the glass forming ability of the alloy increases,and the precipitation amount of B2-CuZr increases.At 930°C,with the the increase of constant temperature time,the atomic clusters in the melt increase,which promotes the precipitation of B2-CuZr and decreases the glass forming ability of the alloy.It is beneficial to regulate the microstructures of amorphous alloy by constant temperature treatment at low temperature above the liquidus.According to the needs of amorphous alloy microstructural control,the optimal quenching process is water quenching after 930°C for 5 minutes under the experimental conditions.Secondly,Φ5mm（Cu0.5Zr0.5）100-XAl X（X=6,7,8,9）,（Cu0.46Zr0.46Al0.08）100-XTa X（X=0,0.25,0.5）and Cu₄₆Zr₄₆Al₈ alloy samples with different diameters were prepared by water quenching after 930°C for 5min.The experimental results show that the increase of Al content does not significantly improve the glass forming ability of the alloy at low temperature,but significantly inhibits the decomposition of B2-CuZr,and the effect of 8at.%Al is the best.0.25at.%Ta can slightly improve the glass forming ability of Cu₄₆Zr₄₆Al₈ alloy.With the decrease of sample diameter,the precipitation and decomposition of B2-CuZr in Cu₄₆Zr₄₆Al₈ alloy quenched at low temperature decrease.With the decrease of holding time at low temperature,the precipitation of B2-CuZr in Cu₄₆Zr₄₆Al₈ alloy decreased.Under this process condition,optimizing the alloy composition is an important measure to inhibit the B2-CuZr decomposition in the low temperature quenching process.Controlling the cooling rate and constant temperature treatment time at low temperature is an important way to control the precipitation amount and distribution uniformity of B2-CuZr in the low temperature quenching process.On this basis,theΦ3-5mm Cu₄₆Zr₄₆Al₈amorphous composites with the single precipitated B2-CuZr are preparated,and the compressive strength and plasticity of theΦ4mm alloy sample are 2089MPa and 3.68%,respectively.Finally,the mechanism of constant temperature treatment above the liquidus affecting the precipitation of B2-CuZr was discussed.Due to the low temperature constant temperature treatment increases the precipitation amount of B2-CuZr phase,the B2-CuZr phase retained to room temperature increases under the same decomposition rate of B2-CuZr.It is also possible that the agglomerated B2-CuZr interface hinders the transformation of B2-CuZr to Cu10Zr7 and CuZr2,thereby inhibiting the decomposition of B2-CuZr phase.It is pointed out that the main reason for the agglomeration of B2-CuZr in the prepared samples is the poor thermal conductivity of the thick-walled quartz tube encapsulating the samples,which leads to the poor quenching of the water medium.The cooling rate and the B2-CuZr distribution uniformity of cross section will be improved by changing the water quenching samples in quartz glass tube to water cooling copper mold quenching alloy melt.It is expected to realize the low temperature copper mold casting and continuous casting of B2-CuZr/CuZr-based amorphous composites.