氮化鋁與鈦介面相的生成機構與微觀結構的演變

Abstract

本研究係利用解析式掃描式電子顯微鏡(SEM/EDS)與穿透式電子顯微鏡(TEM/EDS)，深入分析不同熱處理溫度的介面微觀結構，並利用Ti-Al-N平衡相圖以及擴散路徑圖，探討AlN與Ti介面微觀結構的演化及生成機構。

AlN與Ti介面處反應主要是由於AlN中的Al與N原子經擴散進入Ti側，而造成在Ti側產生一系列的氮化物與鋁化物。AlN與Ti經1000oC之擴散反應，δ-TiN首先生成在介面處，而α2-Ti3Al會在δ-TiN/Ti介面處產生。隨熱處理時間增加，τ1-Ti3AlN會在δ-TiN反應層中生成，其方位關係為[111]τ1-Ti3AlN//[111]δ-TiN與(1-10)τ1-Ti3AlN//(1-10)δ-TiN。隨著N原子擴散進入α2-Ti3Al，δ-TiN與雙晶結構α2-Ti3Al(N)會在α2-Ti3Al反應層中生成。當N原子進入α2-Ti3Al的八面體間隙位置，會造成τ1-Ti3AlN的生成而形成兩相區(τ1-Ti3AlN+α2-Ti3Al)，其方位關係為[111]τ1-Ti3AlN//[0001]α2-Ti3Al(N)與(0-11)τ1-Ti3AlN//(-1-120)α2-Ti3Al(N)。

AlN與Ti金屬經1300℃擴散反應，其反應生成物從AlN側至Ti側依序為δ-TiN、τ2-Ti2AlN、τ1-Ti3AlN、α2-Ti3Al，與兩相區(α2-Ti3Al+α-Ti)。在兩相區中α2-Ti3Al與α-Ti的方位關係為[0001]α-Ti//[0001]α2-Ti3Al與(1-100)α-Ti//(1-100)α2-Ti3Al。在1400℃反應下，反應生成物τ1-Ti3AlN逐漸消失，而γ-TiAl與層狀結構(γ-TiAl+α2-Ti3Al)生成，其中層狀結構(γ-TiAl+α2-Ti3Al)的方位關係為[011]γ-TiAl//[2-1-10]α2-Ti3Al與(1-1-1)γ-TiAl//(01-10)α2-Ti3Al。比較1500℃與1400℃反應後反應區的差異，並未發現γ-TiAl的存在。

為了進一步研究N原子對於AlN/Ti介面所造成的影響，進行氮化鋁與鈦金屬(箔)在1400℃的擴散反應，可發現γ-TiAl逐漸受到N的影響而產生fiber-like τ2-Ti2AlN。γ-TiAl與τ2-Ti2AlN的方位關係為[110]γ-TiAl//[11-20]τ2-Ti2AlN與(1-1-1)γ-TiAl//(1-10-3)τ2-Ti2AlN。隨著τ2-Ti2AlN的生成而釋放出Al原子，使γ-TiAl變成富鋁相的Ti3Al5。此外在α-Ti(Al, N)受到氮化而形成兩相區(α-Ti+δ-TiN)，α-Ti與δ-TiN的方位關係為[110]δ-TiN//[11-20]α-Ti與(111)δ-TiN//(0001)α-Ti。

The diffusional reaction between aluminum nitride (AlN) and titanium (Ti) was carried out isothermally in argon at temperatures ranging from 1000o to 1500oC. The microstructural characterization and phase development were investigated using analytical scanning electron microscopy (SEM) and analytical transmission electron microscopy (TEM), both attached with an energy-dispersive spectrometer (EDS).

It is well known that the decomposition of AlN and the diffusion of Al and N atoms into Ti gave rise to various reaction layers at the interface. After annealing at 1000oC, a δ-TiN layer was initially formed in the reaction zone between AlN and Ti, and the α2-Ti3Al layer subsequently developed between δ-TiN and Ti. Then an intergranular τ1-Ti3AlN phase was formed in the δ-TiN layer with the orientation relationships [111]τ1-Ti3AlN//[111]δ-TiN and (1-10)τ1-Ti3AlN//(1-10)δ-TiN. The further diffusion of N atoms into the α2-Ti3Al layer led to the growth of δ-TiN and a twinned α2-Ti3Al(N) solid solution, wherein N atoms went to one of the octahedral interstitial sites in an orderly manner upon cooling, resulting in the formation of τ1-Ti3AlN. The orientation relationships between τ1-Ti3AlN and α2-Ti3Al(N) were [111]τ1-Ti3AlN//[0001]α2-Ti3Al(N) and (0-11)τ1-Ti3AlN//(-1-120)α2-Ti3Al(N).

After annealing at 1300oC, an interfacial reaction zone, consisting of TiN, τ2-Ti2AlN, τ1-Ti3AlN, α2-Ti3Al, and a two-phase (α2-Ti3Al + α-Ti) region in sequence, was observed in between AlN and Ti. The α2-Ti3Al region revealed equiaxed and elongated morphologies with [0001]equiaxed//[-1100]elongated and (-1010)equiaxed//(-1-122)elongated. In the two-phase (α2-Ti3Al + α-Ti) region, α2-Ti3Al and α-Ti were found to satisfy the following orientation relationship: [0001]α-Ti//[0001]α2-Ti3Al and (1-100)α-Ti//(1-100)α2-Ti3Al. The γ-TiAl and a lamellar two-phase (γ-TiAl+α2-Ti3Al) structure, instead of τ1-Ti3AlN, were found in between τ2-Ti2AlN and α2-Ti3Al after annealing at 1400oC. The orientation relationship of γ-TiAl and α2-Ti3Al in the lamellar structure was identified to be as follows: [011]γ-TiAl//[2-1-10]α2-Ti3Al and (1-1-1)γ-TiAl//(01-10)α2-Ti3Al. Compared with the reaction zone after annealing at 1400ºC, the γ-TiAl was not found at the interface after annealing at 1500oC.

In the other respective, AlN was bonded with a titanium foil at 1400ºC for up to 1 h in Ar. It was noted that the diffusion of N atoms into the reaction zone played an important role to the microstructural development at the AlN/Ti/AlN interface. The diffusion of N atoms into the reaction zone led to the precipitation of a chopped fiber-like τ2-Ti2AlN in the matrix of γ-TiAl, with [110]γ-TiAl//[11-20]τ2-Ti2AlN and (1-1-1)γ-TiAl//(1-10-3)τ2-Ti2AlN, by substituting N atoms for one-half Al atoms after annealing at 1400oC for 1 h. The released Al atoms, due to the precipitation of τ2-Ti2AlN, resulted in an ordered Al-rich γ-TiAl or Ti3Al5. Furthermore, the α-Ti (Al, N) was nitridized into a lamellar layer (δ-TiN + α-Ti) with [110]δ-TiN//[1120]α-Ti and (111)δ-TiN//(0001)α-Ti.

The microstructural development at the AlN/Ti interface is elucidated with the aid of the Ti-Al-N ternary phase diagram and a modified Ti-Al binary phase diagram. Finally, diffusion paths are proposed for the interfacial reactions at various stages.