晶粒尺寸效應對鈦合金之機械性質影響與微齒輪擠壓加工之成形性分析

Grain Size Effect on Mechanical Properties and Deformability of Titanium Alloy in Micro-gear Squeezing Process

黃宗漢(Zong-han Huang)

指導教授 ： 江卓培

國立虎尾科技大學/工程學院/機械與機電工程研究所/碩士(2014年)

摘要

隨著微元件的發展，微成形加工需求逐漸增多，當尺寸縮小對材料成形性、塑流應力不能以傳統方式來解釋其變形之行為。為了改善微元件結構強度、提升使用壽命，許多的研究開始探討晶粒尺寸效應對材料塑性變形所誘發的晶粒再細化後的機械性質影響，利用微模具對金屬材料產生塑性變形，促使晶粒尺寸的變化來提升機械性質，讓微元件成形時趨近最終產品外型，減少後續的加工提高產品的競爭力。本研究針對二級鈦進行 (1)均質退火熱處理(500~1000˚C)來獲得不同平均晶粒尺寸；(2)在微擠壓實驗中，以微齒輪模具對鈦金屬微擠壓成形所誘發晶粒在細化對其機械性質之影響；(3)以有限元素分析軟體(MSC.Marc2010)進行塑性變形分析，判斷所需之成形力量。
實驗結果可歸納為:(1)二級鈦棒經過均質化退火熱處理，其內部結構700 ˚C晶粒析出α相，約在950˚C析出成β相，而500、600˚C晶粒還未析出；(2)二級鈦棒在α相強度係數(k)與應變硬化指數(n)會隨著平均晶粒增加而增加，但硬度值會下降，當α相轉變成β相時，其硬度值反之上升；(3)二級鈦受到擠壓的速度太快，會造成材料無法充填微齒輪模具底部而出現皇冠形狀，由模擬與實驗結果比較700˚C對微齒輪充填率最佳，未經過均質化退火熱處理對微齒輪的充填率效果較差；(4)二級鈦棒之α相經過微齒輪模具齒根圓之塑性變形後，其機械強度可以到達β相之硬度值，而齒冠圓雖有晶粒細化，但沒有受到模具拘束其外型，而機械強度無法提升。

關鍵字

二級鈦 ； 微成形 ； 晶粒再細化 ； 微齒輪 ； 晶粒尺寸效應

並列摘要

To improve the mechanical properties and service life, Many studies investigating grain refinement effects of mechanical properties and formability in manufacturing micro component, Used molds to plastic deformation of metallic materials, the grain will be refinement and improve the mechanical properties, The aim of this research is to investigate the effect of grain size on the mechanical properties and deformability of titanium alloy in micro-gear squeezing process. Specimens made of Grade 2Ti alloy with diameter 4 mm were annealed to temperature of 500,600,700,80,850,900,1000˚C resulting in different initial grain sizes, The initial mechanical properties and hardness of rods were obtained by means of tensile and micro-hardness test. Design the mold shape of micro-gear. the microstructure in squeezing micro-gear process was obtain the grain refinement. Operating finite element analysis(MSC.marc) to predict the forming force.
The experimental results can be summarized as followed:(1)the microstructure of α-phase can be observed in a range of annealing temperature of 700 to 900˚C and 1000˚C precipitate β-phase. but 500、600˚C grain not precipitates (2)microstructure of α-phase the strength coefficient(K)、strain-harding exponent increased as the average grain size increased, The hardness values decrease, but hardness values increased whenβ-phase precipitates(3) Annealing temperature 700 ˚C micro-squeezing filling rate the best than not homogenizing annealing, but squeezing too fast can cause crown gear(4) When the α-phase plastic deformation, mechanical strength to reach the β-phase hardness values, Although material have grain refinement, but grain structure does not accumulate enough strength.

並列關鍵字

Gr.2 Ti ； microforming ； grain refinement ； micro-gear ； effect grain size

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