| Bulk metallic glasses(BMGs)are one of the most promising materials at the present stage.They have superior strength and hardness properties,compared to crystalline alloys,ceramics and polymers.However,application of BMG on engineering is restricted by low ductility.It is important to improve plasticity of BMG at room temperature.This project researched widely used Zr-based BMG,Zr41.2Ti13.8Cu10Ni12.5Be22.5(vitl),by LSP and annealing treatment with heat preservation time.BMG was subjected to X-ray diffraction(XRD)to detect the degree of crystallinity and to judge whether it was still amorphous alloy after treated by two kinds of technical means;Differential Scanning Calorimetry(DSC)confirmed the glass transition temperature and crystallization temperature of Zr-based BMG and determined the appropriate annealing temperature range.Through the uniaxial compression experiments,compressive stress-strain curves were obtained to compare the compressive plasticity and compressive strength of BMG.Scanning electron microscopy(SEM)was used to study the fracture morphology of Zr-based BMG,and microhardness tester tested its hardness value.Firstly,the plastic size-dependence of Zr41.2Ti13.8Cu10Ni12.5Be22.5 cylindrical amorphous alloys was researched.With different aspect ratios,2:1 and 1:1,two groups of columnar amorphous alloy samples were selected,? 6×12 mm and ? 6×6 mm.It was confirmed by compression experiments that the plasticity of vitl BMG gradually decreased with the increase of aspect ratio.After that,vitl BMG was treated by LSP.It was demonstrated that plastic size-dependence,as well as strength size-dependence is inherited after LSP treatment.In addition,the effect of LSP on the compression plasticity and compressive strength of vitl BMG also presents size-dependence.That is,the smaller the aspect ratio of the BMG,the more significant the increase effect of compressive plasticity and strength.The compressive plasticity and compressive strength of vitl BMG at different annealing temperatures were compared to research the effect of annealing treatment on the compressive properties of BMG.It is concluded that,according to the annealing temperature,annealing treatment can improve the compressive properties of BMG to different extents.At the same annealing temperature,for the BMG specimens with larger aspect ratio,the improvement effect is not obvious.Both LSP and annealing treatment with different annealing temperatures but the same annealing time,can enhance the ductility of BMG.The compression properties of vitl BMG were compared by the two kinds of technique.It showed that there were different effects on compressive strength and plasticity under different annealing temperatures.In the four annealing temperatures(483 K,553 K,583 K,623 K),as the annealing temperature increased,the incremental plasticity and strength of vitl cylindrical metallic glass gradually increased.Compared with annealing treatment,LSP had a better effect on the compressive plasticity of vitl BMG.The effects of LSP and annealing treatment on the hardness of BMG were compared.It is found that both LSP and annealing treatment can soften BMG in varying degrees.The softening region of LSP is smaller,while the effect is more obvious.As the annealing temperature increases,the degree of softening of the BMG increases.Under the annealing temperature of 623 K,a small amount of crystal nucleus appeared inside BMG,which formed a composite structure with amorphous alloy,resulting in dispersion strengthening and hardening.The common effects of LSP and annealing treatment on compressive properties and hardness of BMG were studied.The effect of annealing after laser shock peening on compressive plasticity and compressive strength was similar to the as-cast BMG almost.It shows that the two conflicting effects cancel each other out within BMG.For the hardness of BMG,the combined effect of both LSP and annealing heat treatment on the hardness change of BMG is more pronounced than that of BMG caused by a single technical treatment. |
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