Hf对Zr-Al-Ni-Cu金属玻璃弛豫行为的影响

Influence of Hf on Relaxation Behavior of Zr-Al-Ni-Cu Glassy Alloys

通过测定快淬态和退火态比热与温度的关系,研究了Hf元素对Zr_(70)Al_(7.5)Ni_(8)Cu_(14.5)(70Zr)、Zr_(55)Al_(10)Ni_(5)Cu_(30)(55Zr)和(Zr_(0.75)Hf_(0.25))_(65)Al_(7.5)Ni_(10)Cu_(17.5)(65Zr_(0.75)Hf_(0.25))厘米级金属玻璃焓和硬度弛豫的影响。结果显示:70Zr和55Zr合金的结构弛豫表现为单峰现象,在退火温度(T_(a))接近玻璃转变温度(T_(g))时出现弛豫峰;而65Zr_(0.75)Hf_(0.25)合金的结构弛豫表现为双峰现象,分别在523和648 K(接近T_(g))时出现焓弛豫峰。70Zr和55Zr合金在T_(g)温度附近出现明显的单峰弛豫行为,表明合金在T_(g)之前的整个温度范围内具有较高的抵抗退火诱导结构弛豫的能力;另一方面,65Zr_(0.75)Hf_(0.25)合金在523 K附近出现一个弛豫子峰,可能是由于Zr-Hf原子对的键合性较弱,混合焓接近于零,随后在T_(g)附近出现明显的主弛豫。65Zr_(0.75)Hf_(0.25)和(Zr_(0.5)Hf_(0.5))65Al_(7.5)Ni_(10)Cu_(17.5)(65Zr_(0.5)Hf_(0.5))合金的硬度也表现出类似的双峰现象,导致第一峰的T_(a)与焓弛豫峰的T_(a)一致。结果表明,满足非晶形成三原则的Zr、Al、Ni和Cu组成的类二十面体中程有序结构在低T_(a)温度下保持稳定;只有背离非晶形成三原则的65Zr_(0.75)Hf_(0.25)和65Zr_(0.5)Hf_(0.5)金属玻璃焓弛豫和硬度弛豫出现了双峰,表明形成大块金属玻璃非必要组元的增加将导致合金结构在低温退火过程中的不稳定性。

The influence of Hf element on enthalpy and hardness relaxation behavior of Zr_(70)Al_(7.5)Ni_(8)Cu_(14.5)(70Zr),Zr_(55)Al_(10)Ni_(5)Cu_(30)(55Zr)and(Zr_(0.75)Hf_(0.25))(65)Al_(7.5)Ni_(10)Cu_(17.5)(65Zr_(0.75)Hf_(0.25))bulk glass-type alloys with large diameters of centimeter-level was examined by measuring the temperature dependence of apparent specific heats in as-spun and annealed states.Results show that the structural relaxation of 70Zr and 55Zr alloys occurs through a single-stage mode where the relaxation peak is observed at the annealing temperature(T_(a))near glass transition temperature(T_(g)),while 65Zr_(0.75)Hf_(0.25) alloy shows a double-stage reaction with enthalpy relaxation peaks appearing at 523 and 648 K near T_(g).The single-stage relaxation mode for 70Zr and 55Zr alloys indicates that these alloys have high resistance to annealing-induced relaxation over the whole temperature range up to T_(g),because the distinct relaxation occurs only around the temperature of T_(g).65Zr_(0.75)Hf_(0.25) glassy alloy shows a relaxation sub-peak around 523 K presumably due to the weaker bonding nature of Zr-Hf atomic pair with nearly zero in heat of mixing,and the distinct main relaxation occurs near T_(g).The Vickers hardness also shows the similar double-stage peak behavior as a function of T_(a) for 65Zr_(0.75)Hf_(0.25) as well as(Zr_(0.5)Hf_(0.5))65-Al_(7.5)Ni_(10)Cu_(17.5)(65Zr_(0.5)Hf_(0.5))alloys,so the T_(a) for the first-stage hardness peak agrees with that for the enthalpy relaxation.These results imply that icosahedral-like medium range ordered structure consisting of Zr,Al,Ni and Cu elements with the three components rule for stabilization of supercooled liquid remains stable during the low T_(a) relaxation.The double-stage enthalpy and hardness relaxation only appear in 65Zr_(0.75)Hf_(0.25) and 65Zr_(0.5)Hf_(0.5) glassy alloys which deviate from the three components rule,implying that the unnecessary multiplication for the formation of bulk glassy alloys leads to an increase in structural instability during low-temperature annealing.