Please use this identifier to cite or link to this item:
Effect of two-stage hot-pressed sintering on the mechanical properties of silicon carbide
|Authors: ||Tan, Yung-Chun|
|Contributors: ||NTOU:Institute of Materials Engineering|
silicon carbide (SiC);anti-ballistic ceramic;hot-pressed sintering;two-step sintering
|Issue Date: ||2017-05-24T08:17:43Z
|Abstract: ||本研究乃利用添加不同配比之燒結助劑(B4C+C)於碳化矽(SiC)粉末內，並於不同溫度下進行熱壓燒結(壓力24 MPa)來製備碳化矽陶瓷試樣(簡稱BC-SiC)，其中，燒結助劑配比之變化則將在硼的添加量固定，改變不同的碳添加量。先藉由傳統熱壓燒結方式來試驗燒結溫度、碳-硼燒結助劑配比、燒結後試樣之緻密度及其機械性質變化關係。之後，經由此傳統熱壓燒結實驗結果選擇T1溫度(能得到高度緻密化的燒結溫度)來進行兩階段熱壓燒結，用以製備高緻密化碳化矽試件。前後兩種燒結後之試樣均進行樣品密度量測、維式硬度量測以及四點靜壓撓曲強度(flexural strength)試驗、X光繞射儀(XRD)分析、掃描式電子顯微鏡(SEM)與光學顯微鏡(OM)表面形貌觀察。 對於傳統熱壓燒結試驗，由實驗結果顯示，不管添加2 wt%、3 wt%和4 wt%之碳的BC-SiC，熱壓燒結溫度低於2150ºC時，經XRD分析得出，燒結後之碳化矽呈現6H相結構。再者，於2050ºC傳統式熱壓燒結後達到高度緻密化(即相對密度達一數值後，其值不再隨著燒結溫度之升高而增加)。當燒結溫度提升至2150ºC後，有大量的6H轉變為4H相發生。在此高溫下燒結，由於4H相的出現，碳化矽明顯有異向性的晶粒成長，產生長軸晶粒。 在兩階段熱壓燒結時，當燒結溫度先達2050ºC後即降至2020ºC，添加3 wt%碳的BC-SiC能得到高的相對密度(99.2%)以及高的硬度(27.61±1.41 GPa)，四點彎曲強度之數值為430.3±5.1 MPa，破裂韌性強度之數值為3.07±0.07 MPa•m1/2。適當的碳添加之輔助，可使碳化矽緻密化使其具有良好的機械性質。而且使用兩階段熱壓燒結，先升溫在較高溫度下，由於高燒結驅動力，提高緻密化速度，而後並在較低溫度下進行最終緻密化的燒結，達成高緻密度之效果。研究結果顯示，利用兩階段熱壓燒結製備出來的BC-SiC相較於傳統式熱壓燒結，能在較低持溫燒結溫度擁有較高硬度、四點彎曲強度與緻密度，呈現較佳的機械性質表現，對於未來防彈裝甲之應用是一個非常優異的材料製程。|
The research aims to fabricate the body of silicon carbide (SiC) ceramic material (so-called BC-SiC) using a hot-pressed sintering method performed jointly with sintered aids (B4C+C) of various ratio (0.6 wt.% B+ 2~4 wt.%C) under distinct sintering temperatures (1950~2150ºC). Here, the ratio of additives was varied by altering the added content of carbon (2 4 wt.%) with the fixed content of boron (0.6 wt.%). A conventional hot-pressed sintering was firstly performed to try out the relationship among the sintering temperature, the ratio of additives and the densification of sintered body as well as its mechanical properties. Next, a two-step hot-pressed sintering was executed to prepare the BC-SiC body of high densification, where the T1 temperature of two-step hot-pressed sintering was selected by the previously conventional hot-pressed sintering experiment T1 is the temperature that could attain high densification of BC-SiC. Both of the sintered ceramic bodies were separately carried out the measurement of density and Vickers hardness, the test of flexural strength, and x-ray diffractometer (XRD) examination as well as the observation of optic microscope (OM) and scanning electron microscope (SEM). For the conventional hot-pressed sintering experiment, the results showed that the BC-SiC body displayed the structure of 6H phase from XRD analysis after sintering at the temperature lower than 2150C, regardless of the carbon addition of 2 wt.%, 3 wt.% or 4 wt.%. Furthermore, the high densification of BC-SiC was achieved after sintering at 2050C where the relative density reached a high value and the value didn’t increase with further increasing the sintering temperature. When the sintering temperature increased to 2150C, there were appreciable amounts of 4H phase which was transformed from 6H phase appeared in the sintered specimen. Upon the sintering of 2150C, an anisotropic grain growth of BC-SiC apparently occurred and the morphology displayed long axis grains due to the formation of 4H phase. As for the two-step hot-pressed sintering, the sintered body of BC-SiC with the addition of 3 wt.% carbon could attain high relative density of 99.2% and high Vicker’s hardness of 27.61±1.41 GPa when the sintering temperature firstly increased to 2050C and then decreased immediately to 2020C. The measured flexural strength of the BC-SiC was 430.3±5.1 MPa and the evaluated fracture toughness was 3.07±0.07 MPa•m1/2. It suggested that the sintering assistant of carbon with proper addition content could promote the high densification of BC-SiC which was possessed of good mechanical properties. Besides, upon the two-step sintering, firstly increasing the sintering temperature to higher temperature could quickly densify the BC-SiC due to high driving force of sintering, and then the high densification of BC-SiC was achieved when the sintering was sustained at lower temperature. Consequently, compared with the conventional hot-pressed sintering, the BC-SiC body prepared by the two-step hot-pressed sintering was possessed of high hardness, flexural strength and densification after lower temperature of sintering, and showed better performances of mechanical property than that of the conventional hot-pressed sintering at the same temperature of dwelling. It would be an excellent process of ceramic materials fabricated for the application of anti-ballistic armour.
|Appears in Collections:||[材料工程研究所] 博碩士論文|
Files in This Item:
All items in NTOUR are protected by copyright, with all rights reserved.