The Preparation And Properties Of Mg-Ni Amorphous Alloys

Amorphous alloy （also known as metallic glass） has lots of superior properties whichtraditional metal materials can not match with due to their own unique structural features, thusbecoming one of those structural materials in the special field. Compared with otheramorphous alloy, Mg-based amorphous alloy are rapidly receiving attention due to their highspecific strength, low cost and the abundance of magnesium and other unique advantages, andMg-based amorphous alloy have gradually become one of intensive research topics in thefield of materials.In recent years, there are two methods mainly to obtain Mg-based amorphous alloys withhigh glass formation ability:（1） adjustment of the ratio of the elements in the alloy;（2）micro-alloying. The addition of mircoalloying element is proved to be one of those effectivemeans to improve the glass formation ability （GFA） of Mg-based amorphous alloys. Rapidlysolidified alloy and microalloying are used into Mg-based amorphous alloys flexibly in thiswork. Mg-Ni-Y ternary amorphous alloys with different compositions were obtained by asingle-roller melt-spinning technique, and some samples were annealed in different processconditions. Then Mg-Ni-Y-Ce、Mg-Ni-Y-Nd quaternary amorphous alloys were prepared byusing cerium and neodymium to partially substitute for yttrium. Phase identification,crystallization behaviour and glass forming ability （GFA） were investigated by X-raydiffraction （XRD） using a Rigaku D/max with Cu Kα radiation, differential thermal analysis（DTA, NETZSCH409） technique at a heating rate of20K/min （in flowing argon） andscanning electronmicroscope （SEM）. The mechanical properties and the corrosion resistanceof the amorphous alloys were studied by microscopic vickers hardness tester andelectrochemical workstation.According to the results of XRD, DTA and microhardness test, the GFA themicro-hardness of Mg_86.33Ni_13.67-xY_x（x=0,1,3,6,10） is improved successfully with increasingof Y addition. The highest GFA appeared at x=6, while it slightly decreased with furtherincreasing of Y; the position of the main diffraction halo is different for the alloys, and it wasshown by crystallization treatment that the maximum of the main diffraction halo of alloyswith x=0,1,3corresponds to the main peaks of a metastable fcc-Mg₆Ni or fcc-Mg₆Ni+Ni-Y intermetallic phases, and for the alloys with x=6,10, it corresponds to Mg-Y and Ni-Yintermetallic phases; the corrosion resistance of the amorphous alloy is increased withincreasing small amount of Y addition in neutral NaCl solutions, while decreased with moreaddition of Y. The corrosion resistance of amorphous alloy is related to structure andcomposition.The GFA of Mg65Ni25Y10amorphous alloy is the highest by investigating theMg80-xNi10+xY10ternary alloys. Based on Mg65Ni25Y10ternary alloy, suitable amount ofcerium and neodymium elements were added into Mg-Ni-Y amorphous alloy, which wereMg₆₅Ni₂₅Y_10-xCe_xx（x=0,2.5,5,7.5,10） and Mg₆₅Ni₂₅Y_10-xNd_x（x=0,2.5,5,7.5,10）, and theglass formation ability was improved to varying degrees. All the critical speed ofMg₆₅Ni₂₅Nd₁₀and Mg65Ni25Nd10amorphous alloy is lower than7.693m/s. Compared with Ce,the effect of Nd on the glass formation ability of Mg-based amorphous alloy is moresignificant and effective. The corrosion resistance of the amorphous alloys is increased withincreasing Ce addition in0.01mol/L NaCl solutions, while the corrosion resistance isdecreased with increasing Nd addition. It might be caused by difference in the stucture ofCerium oxide and Neodymium oxide.In the process of annealing for lower temperature, with increasing annealing temperaturegradually,2θ value corresponding to the maximum intensity of the amorphous diffusescattering peaks increases gradually, indicating the decrease of the distance between thenearest neighbor atoms in clusters and the occurrence of structural relaxation in theamorphous alloy, resulting in the decrease of topological instability. By analyzing the resultsof crystallization treatment, the crystallization of Mg_86.33Ni_12.67Y₁takes place in two stages.At the first stage of crystallization, Mg₆Ni and Ni7Y2are precipitated; and at the second stage,the meta-stable phase fcc-Mg₆Ni transforms into eutectic products including the equilibriumα-Mg and Mg2Ni phases. Meanwhile C36-type Laves phase MgNi₂are precipitated in thesurplus glass matrix. The micro-hardness changed significantly with annealing temperatures,it was accompanied by the interplay between the change of free volume and precipitatesduring the annealing process.