鈦生胚電極之放電披覆發色技術開發

Abstract

表面工程的功能與目的便是利用不同的表面改質技術以增進基材的特殊性質。本研究便是藉由利用放電披覆與氧化反應，將自行壓製的純鈦生胚電極，於去離子水中對SUS304不鏽鋼工件進行放電披覆發色。實驗中主要針對放電電流、放電脈衝時間及工作因子對披覆層中不同表面特性進行探討，包括披覆層厚度、表面粗糙度、表面硬度、表面狀態及顏色顯現，並將不同放電參數對披覆層形成機制作歸納。

研究結果顯示，提高放電電流會因放電能量變大而使厚度變厚，但也會因熔融組織的單位體積變大而使表面粗糙度變差，並會在表面形成凸起凝固體點及凸緣。放電脈衝時間在31μs以下，所披覆之厚度會隨放電持續時間增加而變大，但表面粗糙度則會隨著放電脈衝時間的拉長而變差。當Duty factor由0.33變為0.5時，其厚度會隨之增加，但當再改變為0.8時，披覆層厚度便會因有效放電次數減少而又下降，而Duty factor越大，表面粗糙度則會越差。披覆層硬度則會隨著披覆層厚度的變厚而變大。綜合而言，我們歸納出放電電流主要影響粉末熔漿量及單位粉末熔漿的尺寸，放電脈衝時間則會決定影響電極熔融的極間溫度，Duty factor則會影響粉末熔漿的冷卻模式。

The function and purpose of surface engineering utilizing various kinds of surface modification techniques are to improve the particular properties of the workpiece. In this research, we propose a new surface coloring treatment, utilizing Electro-Discharge Coating (EDC) and oxidation, to make the oxide layers piled up on the SUS304 stainless steel substrate in the distilled water by using Ti powder green compact electrode. The following characteristics of the surface layers were investigated in this study: thickness, roughness, hardness, surface condition, and color tone. During this process, the effects of peak current, pulse duration, and duty factor were discussed respectively.

The results revealed that the higher peak current can make the thickness of oxide layers thicker due to the larger discharging energy, and it would make the surface roughness worse, owing to the larger unit volume of melting metal and the formation of the dendritic precipitates. As the pulse duration time was under 31μs, the thickness of oxide layers would grow with the increasing pulse duration time. The surface roughness would get worse with the elongation of pulse duration time. The value of duty factor turned from 0.33 to 0.5, the thickness of the layers would get thicker thereupon, but when the duty factor became to 0.8, the reducing number of effective discharge would make the layers thinner. When the thickness of the surface layers became thicker, an increasing of the surface layers hardness was observed. As a conclusion, peak current affected the amount and the dimension of the melting powder mainly, pulse duration time would influence the temperature of the gap, and the cooling time were decided by duty factor.