製備鈦及鈦鎳合金之粉末冶金製程研究

Powder Metallurgy Processes of Ti and TiNi Alloys

吳筱涵(Shiau-Han Wu)

指導教授 ： 黃坤祥

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00574

摘要

金屬射出成形( Metal Injection Molding, MIM )，具有一次製作出淨形或近淨形，加工步驟簡化、廢料少等優點，對於提煉成本高、加工不易的鈦和鈦鎳合金而言，是一種相當有優勢的製程選擇。由於Ti粉粒徑尺寸偏大不易粉碎，而氫化後的TiH2顆粒硬脆，可用以製作小粒徑之粉末，同時此粉末在室溫穩定不易氧化、價格便宜，故本研究主要目的為評估將TiH2粉末應用在MIM製程的可行性，並與Ti粉加以比較。
本實驗藉由熱脫脂製程參數的最佳化以降低碳污染，熱脫脂後的試片其碳含量大約為0.08wt%，符合ASTM碳含量小於0.1%的標準。燒結時，以高真空(10-4~10-5torr)環境，在石墨真空爐中，試片加蓋並加入吸氧用之TiH2粉以阻擋爐中污染，燒結溫度1100℃持溫兩小時，碳含量可維持在0.08wt%左右。
不論是乾壓成形或者是MIM所得之試片，TiH2試片燒結後，燒結密度均可達 98%。然而拉伸試驗的結果顯示，以TiH2做為起始粉末，燒結後的試片幾乎沒有延展性，抗拉強度僅160MPa左右。若以Ti粉取代TiH2粉，乾壓成形燒結後的試片其伸長量大幅增加至11%，強度為360MPa。不過以MIM製程所得之試片其延展性卻不佳(伸長量4%，強度360MPa)。碳氧含量方面，TiH2試片反而比Ti高，表示TiH2在製程中較易受到污染，MIM試片比乾壓成形高，表示黏結劑為主要污染來源。
本實驗亦嘗試將TiH2和Ni粉配製TiNi形狀記憶合金進行乾壓成形和燒結製程，實驗發現，在一般認為TiNi原子數1:1的最佳比例時，卻沒有最佳記憶效應(ΔH=13.4J/g)，反而發現在Ti略多(>50at%)的情形下，才會有最佳的形狀記憶效應。推測其原因和在燒結製程中Ti2Ni的形成有關，粉末交互擴散的過程中，Ti2Ni的形成能吸附製程中碳氧等雜質，使得基地的TiNi相純度較高。但Ti2Ni出現，易使TiNi相呈富Ni狀態，影響記憶效應，故Ti的比例稍微提高，析出足夠Ti2Ni吸附雜質，能使TiNi相純度提高，展現記憶效應。實驗結果顯示，以TiH2為起始粉末，Ti-44.92at%Ni(Ti-50wt%Ni)有最大之ΔH約為23.8J/g，若以Ti為原始粉，在Ti-49at%Ni的比例下，ΔH有最高值，約為28.7J/g。

關鍵字

金屬粉末射出成形 ； 粉末冶金 ； 燒結 ； TiH2粉 ； TiNi ； 形狀記憶合金

並列摘要

The metal injection molding (MIM) process has been applied to produce net-shape or near net-shape parts due to its advantages of fewer processing steps and waste. It is particularly attractive to Ti alloys due to their machinability.
Generally speaking, it is difficult to make fine Ti powders. However, fine TiH2 particles can be produced brittle enough to be pulverized easily. It is also chemically stable and inexpensive. If TiH2 powder can be used in the MIM process, it will open up Ti alloy market. The challenge of this thesis is thus to find a way.
In order to alleviate the contamination, it is necessary to optimize the thermal debinding parameter. In this study, the lowest carbon content after thermal debinding was about 0.08wt% ,which meets the ASTM standard (<0.1wt%). For sintering, specimens were sintered in a boat with cover at 1100℃ for 2 hours in high vacuum environment (10-4~10-5torr) in the graphite vacuum furnace. The carbon content of the as-sintered specimen still maintained about 0.08wt%.
Both pressed and MIM part that were made of TiH2 powders were brittle and weak. The elongation was about 0.94% and the tensile strength was about 160MPa. Dry compacts using Ti powders instead of TiH2 had much higher ductility and strength 11% of elongation,and 360MPa strength. But, the elongation was reduced to 4% when MIM process was employed. The results also indicated that TiH2 was to be more prone to reactions with carbon and oxygen than did Ti. Moreover, the MIM part had higher carbon and oxygen content than did the dry compact. The impurities mainly came from the binder system.
TiNi shape memory alloy (SMA) was also prepared with TiH2 and Ti powder. Ti-50at%Ni that was made of TiH2 powder showed weak shape memory effect (SME, ΔH=13.4J/g). A little more Ti over 50at% in SMA improved the SME, probably due to the presence of Ti2Ni. This is probably because Ti2Ni could absorb carbon and oxygen during the process and purifies TiNi. The other reason was that the TiNi matrix becomes Ni-rich and not uniform when Ti2Ni existed in Ti-50at%Ni. Thus, to improve the SME, increasing Ti content slightly helps producing more TiNi phase. The results showed that Ti-44.92at%Ni (Ti-50wt%Ni) using TiH2 powder had an improved latent heat (ΔH=23.8J/g) and Ti-49at%Ni that were made of Ti powder had the highest latent heat(ΔH=28.7J/g).

並列關鍵字

Metal injection molding (MIM) ； powder metallurgy (PM) ； sinter ； TiH2 ； TiNi ； shape memory alloy (SMA)

參考文獻

[26] H. C. Lin, K. M. Lin, and Y. C. Chen, “A Study of Mechanical Machining of TiNi Shape Memory Alloys”, Chinese Journal of Materials Science, 1999, Vol. 31, pp. 28-34.

[6] M. Ma, D. Wang, W. Wang, X. Hu, X Jin, and G. Z. Chen, “Extraction of titanium from different titania precursors by the FFC Cambridge process”, Journal of Alloys and Compounds, 2006, Vol. 420, pp. 37-45.

[8] Y. Li, X. M. Chou, and L. Yu, “Dehydrogenation Debinding Process of MIM Titanium Alloys by TiH2 Powder”, Powder Metallurgy, 2006, Vol. 49, No. 3, pp. 236-239.

[9] V. Bhosle, E. G. Baburaj, M. Miranova, and K. Salama, “Dehydrogenation of Nanocrystalline TiH2 and Consequent Consolidation to Form Dense Ti”, Metallurgical and Materials Transactions A, 2003, Vol. 34A, pp. 2973-2799.

[11] K. S. Weil, E. Nyberg, and K. Simmons, “A New Binder for Powder Injection Molding Titanium and Other Reactive Metals”, Journal of Materials Processing Technology, 2006, Vol. 176, pp. 205-209.