本研究以Ti/Si/C作為起始粉末於1atm氬氣及25MPa之機械壓力下進行熱壓燒結，藉由改變起始粉末中之Si含量與燒結溫度，探討此因素對於TiC/Ti3SiC2複合材料之相組成、微結構與機械性質的影響。實驗結果顯示，隨著起始粉末中之Si含量減少，反應生成之第二相TiC含量會增加，且當溫度超過1550℃後，會隨著溫度的增加造成Ti3SiC2分解，產生TiC。為了比較第二相含量對於機械性質之影響，本研究固定1850℃持溫30分鐘之熱壓燒結參數，並控制起始粉末之Si含量，以3Ti/1,0.9,0.8,0.7Si/2C的莫耳比作為起始粉末，可得一系列不同含量且緻密化的TiC/Ti3SiC2複合材料。

將此一系列不同第二相含量的複合材料進行機械性質之分析，結果顯示隨著第二相含量的增加，材料的強度會上升，當第二相TiC之含量為14.5vol%時，具有最高之四點抗彎強度，其值為425MPa，與純相Ti3SiC2材料相比，強化了約42%。強化的原因為晶粒細化與破壞模式的改變，將裂縫導向穿晶破壞為主。但當第二相含量超過14.5vol.%後，強度會隨著第二相含量的增加而下降，造成此現象的主因為熱應力造成殘留孔洞，使得強度值下降。

利用SENB法量測之韌性值方面，在TiC含量增加的初期並不會差異太大，且最高可達7.2±0.4MPa‧m1/2，由SEM斷面之觀察可發現此複合材料仍有本質之Ti3SiC2韌化行為，如微裂縫、脫層、層板破壞、晶粒扭曲與糾結帶產生等。且第二相幫助韌化之行為亦可發現，如裂縫轉折、裂縫分支、晶粒架橋與晶粒拔出等，因而擁有比純相Ti3SiC2更好的韌性行為。當第二相含量繼續增加而超過14.5vol％後，會因破壞模式改變，導致韌性值下降。

硬度值則隨第二相的含量增加而增加，最高可達6GPa，與純相Ti3SiC2相比，提升約50%。

In this investigation, Ti / Si / C powders are used as starting materials and hot pressed under mechanical pressure of 25MPa. By controlling the starting molar ratio of Si and sintering temperature to investigate how these factors influence the phase, microstructure, and mechanical properties of this TiC/Ti3SiC2 composites system. Results show that with the starting molar ratio of Si decreasing, the formation of TiC will increase. In addition, when sintering temperature above 1550℃, Ti3SiC2 will decompose into TiC and Si causing the content of TiC increase with the temperature increasing. In order to investigate how the second phase influence mechanical properties, the starting molar ratio of Si is controlled and use 3Ti/1,0.9,0.8,0.7Si/2C as starting materials to hot pressed at 1850℃ for 30minutes under mechanical pressure of 25MPa.

Experimental results show that 4-p bending strength will increase with the content of second phase increasing, and the value of strength is 425Mpa when the composites content 14.5vol% TiC. Compare with monolithic Ti3SiC2, the strength improved 42%. The reason of better strength is contributed to grain size reduction and transgranular fracture. However, the reduction of strength will be observed when the content of TiC over 14.5vol%. The reason is the appearance of pores causing by the difference of thermal expansion coefficient.

The value of fracture toughness is similar in the beginning of TiC content rising, and the value reaches 7.2±0.4MPa×m1/2. By SEM observation of fracture surface, the Ti3SiC2 intrinsic toughening mechanism such as microcrack, laminate fracture, buckling and delamination within grains, kink band formation was observed. In addition, second phase toughening mechanism such as crack deflection, crack branching, crack bridging and grain pull out are another reasons causing the fracture toughness value better than monolithic Ti3SiC2. Unfortunately, the value of fracture toughness will decrease when the content of TiC over 14.5vol% because of the behavior of fracture changing.

The value of hardness increase with TiC content increasing, and reach to 6GPa, 2 times better than monolithic Ti3SiC2.

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