請問鈦金屬於885度時結晶結構變化?是什麼意思?

Question

請問鈦金屬於攝氏885度時結晶結構變化?是什麼意思?結晶結構變化指的是什麼?實質的影響是什麼?強度變弱嗎?還是會變形?超過885度後就沒事了嗎?小弟是外行人,懇請詳答!

Answer 1

純鈦在883 oC以下原子是呈六方最密堆積結構( HCP )堆積, 超過883oC則變成體心立方堆積( BCC), 因此會有體積上的變化,後果是變形. 如果製件形狀複雜,伴隨的應力集中甚至會讓製件破裂.
所以鈦雖然比重輕,但是不適合在高溫環境下使用.

Answer 2

請參考這篇文章:

鈦合金

http://pubs.acs.org/cgi-bin/abstract.cgi/iechad/1950/42/i02/f-pdf/f_ie50482a012.pdf?sessid=6006l3

A polymorphic metal, titanium has a hexagonal, close-packed
crystal structure at normal temperatures, but changes to a bodycentered
cubic structure above about 885" C.

一種具多形態的金屬,鈦於常溫是一種六方最密堆積晶體結構(hcp),但超過大約885度 C就轉變為體心立方結構(bcc)的晶型

This offers an opportunity for development of properties by heat treatment of some alloys. However, interesting and useful as the transformation
may be, it adds complexity to alloying considerations.

這個現象提供了藉由熱處理某些鈦合金以發展新性質的機會
然而,即便這種晶型轉變現象是多麼地有趣又有用,它的確是增加了在處理合金時,要考慮的問題的複雜性

以下是一篇利用鈦金屬的晶型轉變現象於鈦合金抗腐蝕現象之研究報告:

IN-VITRO CORROSION RESISTANCE STUDY OF HOT WORKED Ti-6Al-7Nb ALLOY IN A ISOTONIC MEDIUM

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322001000100005

這是其中一段參與合金的金屬與兩種晶型關係之描述:

Pure titanium undergoes an allotropic transformation at about 885 oC, changing from an alpha phase (h.c.p.) to a beta phase (b.c.c.), and the alloying elements may either lower or raise the phase transformation (beta transus) temperature.

Aluminium, as alpha phase stabilizer, is highly soluble in both the a and b phases. Vanadium and niobium are both beta phase stabilizers and also highly soluble in both phases.