論文摘要

本研究利用不同莫耳比TiC : Si =3 : 1與TiC : Si =3 : 2原始粉末，以熱壓燒結方式製備SiC / Ti3SiC2 / TiC陶瓷複合材料。於本系統中，由於起始粉末含有Si (熔點=1414℃)，為避免Si的熔融，本實驗採用兩階段燒結方式，於第一段燒結選用1350℃持溫，之後再升至較高溫度1500℃持溫以達緻密化。

實驗結果發現，在TiC : Si =3 : 2莫耳比參數下會導致生成TiSi2雜相。為降低TiSi2雜相減少Si含量，而在3 TiC /1 Si莫耳比，於1350℃持溫2小時再升至1500℃持溫1小時之升溫參數下，發現可有效去除TiSi2雜相，而製備SiC / Ti3SiC2 / TiC複合陶瓷。

以3 TiC /1 Si莫耳比，兩階段燒結之燒結體進行機械性質(韌性、四點抗彎)的分析，在韌性方面利用SENB方式量測，結果顯示破壞韌性值可達7.1 ± 0.3 MPa‧m1/2，觀察其破斷面可發現，第二相Ti3SiC2以裂縫轉折、晶粒脫層翹曲、糾結帶形成等能量吸收機制達到韌化效果。在強度方面，藉由四點彎曲試驗得知，該陶瓷複合材料之平均強度值為625 ± 27.7 MPa，相較於TiC陶瓷材料(四點抗彎值為420 MPa)，強度有明顯提升，在強度方面可能為強化相SiC所致。

Abstract

SiC/Ti3SiC2/TiC ceramic composites were fabricated by hot-pressed sintering method with different TiC/Si molar ratio. Two step sintering was adopted to avoid Si melting and chosen 1350℃to soak then heated to 1500℃ for densification in this experiment.

The XRD analysis of sintered specimen with 3TiC/2Si (molar ratio) mixture by two-step sintering shows the existence of TiC, Ti3SiC2, SiC and TiSi2 phases. The decrease of Si content in raw powder mixture has successfully eliminated the TiSi2 second phase. The XRD analysis of two-step sintered specimen with 3TiC/1Si (molar ratio) mixture reveals that the primary phases are TiC, Ti3SiC2 and SiC phases.

The value of fracture toughness is 7.1 ± 0.3 MPa‧m1/2 and the SEM fractographs show TiC matrix is toughened by Ti3SiC2 phase addition due to crack deflection, buckling, delamination within individual grain, and kink band formation mechanism. The four-point bending strength of SiC/Ti3SiC2/TiC composite is 625 ± 27.7 MPa higher than pure TiC ceramics (420MPa) due to the strengthening effect of SiC second phase.

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