通过粉末冶金的方法制备高熵合金

POWDER METALLURGY OF HIGH ENTROPY ALLOYS

冯世辉

11749170

硕士

材料工程

余鹏

2019-06-01

2019-06-28

哈尔滨工业大学

深圳

高熵合金作为一种至少含有四种主元的新型多主元合金，因其优异的力学性能以及部分功能性能，高熵合金受到了许多研究人员的关注，而高强度以及硬度造成了加工难度高等特点。本文通过元素粉烧结以及放电等离子烧结的方法分别制备了成分为CoCrFeNi以及Al0.3Cr0.9FeNi2.5V0.1的高熵合金，并对其粉末制备工艺、烧结工艺以及力学性能进行研究，其抗拉强度高达1.6 GPa，优于现有部分高熵合金。研究发现，通过将元素粉混合后烧结的方法可以成功制备出CoCrFeNi高熵合金块体，除样品中出现的少部分Cr元素的化合物外，合金成分均一且无偏析产生。通过该方法制备高熵合金存在一个问题，就是难以形成近乎全致密的样品，且晶粒粗大、力学性能低，并且在合金元素的选取中不能选用易形成高熔点合金化合物的主元（如Al和Ni元素）。但是该方法适用性广、耗时段、成本低，可以轻易改变合金成分，是一种很好的研究高熵合金相形成规律的方法。为制备致密度高、力学性能好的高熵合金，选取现有的合金成分，采用机械合金化+放电等离子烧结的方法制备Al0.3Cr0.9FeNi2.5V0.1高熵合金。在通过球磨的方法制备高熵合金预合金粉体时发现，虽能成功制备相结构为FCC的高熵合金粉末，但该合金成分在球磨过程中易发生冷焊的现象，而在干磨后增加湿磨工艺可以有效缓解该现象并提升粉末产率，同时还可以起到细化粉末的作用。并确定最终球磨参数为干磨48 h+湿磨12 h。在烧结研究中，通过放电等离子烧结的方法制备了Al0.3Cr0.9FeNi2.5V0.1高熵合金块体。发现在1100 oC下烧结的样品致密度最高（99.7%），并且经过600 oC下等温1 h的时效处理后，样品拉伸强度达到1648 MPa。虽然该强度同传统熔炼后轧制所制备的相同合金成分的样品强度相仿，但是本实验中样品塑性较低（<1%）。为分析材料塑性较低的原因，对材料的组结构进行表征，发现在材料中存在大量纳米析出相，虽然增大了材料的强度，但是由于部分晶粒较小且分布不均匀、材料中存在微孔、晶界上的析出相以及BCC结构脆性相的原因，导致材料过早失效。

As a new concept alloy which contains at least four principle elements, high entropy alloys (HEAs) attracted many researchers’ attention due to its extraordinary mechanical properties and some functional properties. In present study, CoCrFeNi and Al0.3Cr0.9FeNi2.5V0.1 HEAs were synthesized by conventional sintering and spark plasma sintering, respectively. The synthesized route, sintering parameters and mechanical properties were researched in this paper. The CoCrFeNi HEAs were successfully prepared by sintering the mixture of element powder, no chemical segregation was founded in sample, despite bits of intermetallic phases of chromium. There is a problem in this method, that is, it is difficult to sinter a sample with near fully-density, crystal grains are coarse and the mechanical properties are not good. In additional, some elements which are easily to form intermetallic phases cannot be used in this method, such as aluminum and nickel. However, this method has many positive characteristics, such as highly applicability with many elements, low time consumption and low cost. Generally, this is a appropriate method to investigate the phase formation rules of HEAs. To synthesis HEAs with high density and good mechanically properties. MA (mechanical alloying) and (spark plasma sintering) were used improve sample density. Al0.3Cr0.9FeNi2.5V0.1 were used in this study. In the section of “powder preparation”, ball-milling were used to synthesis pre-alloyed powder. The pre-alloyed powder with FCC structure were prepared by dry-milling for at least 36 h, however, due to the cold welding effect, productive rate of powder is at a low level. Thus, wet-milling were added after dry-milling, this process also reduces the average size of powders. Finally, the parameter of ball milling process is 48 h dry-milling and 12 h wet-milling was added after dry-milling. In the section of sintering, HEAs can reach highest density (99.7%) under sintering temperature of 1100 oC. After aging treatment (600 oC for 1 h), tensile strength of sample is 1648 MPa. Though tensile strength is similar with the sample prepared by arc melting and cold rolling under the same alloy constituent, sample plasticity is too low (<1%). To explain the poor plasticity, SEM, EBSD, TEM were used to characterize the microstructure of alloys. Although a large amount of precipitations were detected, and increase the strength of materials, the heterogeneous grain size and distribution, brittle BCC phases and micro voids in sample reduces plasticity of materials.

高熵合金 传统烧结 球磨 放电等离子烧结 沉淀强化

high-entropy alloys conventional sintering ball-milling spark plasma sintering precipitation hardening

中文

联合培养

南方科技大学

冯世辉. 通过粉末冶金的方法制备高熵合金[D]. 深圳. 哈尔滨工业大学,2019.