超硬合金의 結合相 組成과 炭化物 粒子 性狀에 關한 硏究 = (A) Study on the composition of binder phase and the morphology of carbide phase in cemented carbides

다국어 초록 (Multilingual Abstract)

The effects of carbon content upon the composition of binder phase and the properties of carbide phase are studied in the alloys of WC-Co, WC-(TiC-TaC-NbC)-Co, TiC-Mo_(2)C-(Co+Ni) base cermet, VC-Co and NbC-Co alloys.
The results obtained are as follows:
1. Composition of binder phase
1) WC-Co and WC-(TiC-TaC-NbC)-Co alloys : The W solute content in binder phase increases with decreasing total carbon content at room temperature. It becomes minimum at the higher carbon limit and maximum at the lower carbon limit of two phase region and remains constant in the three phase region. The maximum values of W/Co in binder phase are approximately 28% and 24% in WC-Co and WC-(TiC-TaC-NbC)-Co alloys respectively, while the minimum values of W/Co are approximately 1.5% in the both alloys. However the solubility of other elements such as Ti, Ta, Nb in the binder phase is neglegible at room temperature.
The binder phase of tungsten carbide-based alloy was studied by the measurement of magnetic saturation. The relationship between specific magnetic saturation(SMS) and W solute content in Co rich binder are as follows:
SMS(%) = 100(1-W/Co(%))
where 1.5 < W/Co < 28 in WC-Co alloy
1.5 < W/Co < 24 in WC-(TiC-TaC-NbC)-Co alloy
The dissolved carbon content in Co rich binder phase decreases with decreasing total carbon of alloy at room temperature.
Reciprocal relationship between dissolved W and C in binder is represented as [W] [C]= 2×10^(-4) where [w] and [C] are given in atomic fraction of W/Co and C/Co respectively in WC-Co alloy.
The carbon range of two phase region depends on Co content of WC-Co alloy and can be represented as follows:
6.13 - 0.07846 Co(%) ≤ Total carbon of alloy(%) ≤ 6.13 - 0.0622 Co(%)
2) TiC-Mo_(2)C-WC-TaC-NbC-(Co+Ni) alloys : As in the case of WC-Co alloy the content of solute element in binder phase increases with decreasing total carbon content regardless of binder composition ratio of Co/Ni at room temperature. Mo and W are soluble in the binder phase of whole range of Co/Ni ratio. But the solubility of Ti, Nb in Co binder is neglegible and increase with increasing the fraction of Ni in binder, while the contents of Mo and W in binder decrease. It can be emphasised that when the alloys have same total carbon content regardless of binder composition of Co/Ni, the sum of concentration of each solute of W, Mo, Ti and Nb in binder shows same values. Maximum atomic ratio of total solute/(Co+Ni) in binder is about 10% at lower carbon limit of alloys. Ta is not dissolved in any of binders.
It is found that the relationship between magnetic saturation and total solute concentration in the binder phase of TiC-based cermet is represented as follows:
S = -9.15 X + 350 (Co Binder)
S = -8.26 X + 251 (Co/Ni=5/5 Binder)
S = -9.34 X + 174 (Ni Binder)
where S is magnetic saturation in Gauss and X is the atomic ratio of total solute/(Co+Ni) in binder. x varies from 11% to 0.
3) VC-Co, NbC-Co alloys : Also in VC-Co and NbC-Co alloys the content of solute elements in binder phase increase with decreasing total carbon content, and there is linear relationship between magnetic saturation and solute concentration in binder.
2. Properties of carbide phase
1) WC in Co rich binder phase : As the total carbon of alloy decreases, the fraction of finer WC grain increases. As a result the average WC grain size decreases.
The important thing is that abnormal growth of WC grain was originated from the coarser WC particles in raw WC material and phase did not have any relation to the formation of abnormal WC grain in this study, which is contrary to some published works of other authors.
The aspect ratio of abnormal WC grain was largely affected by additives of some carbides. The aspect ratio of abnormal WC was over 2.8. TiC rises the value up to 6.0. Mo_(2)C and Cr_(3)C_(2) lowers it up to 2.45.
2) η phase in Co rich binder : The morphology of phase can be affected by sintering temperature, level of carbon deficiency and decarburizing during sintering.
η phase, developed during cooling from the WC + liquid region shows dendritic growth behavior and octahedron shape when fully developed.
The composition of η phase is M_(6)C type. The composition and lattice parameters very when other carbide is added in alloy.
3) VC and NbC in Co rich binder : The content of combined carbon and average grain size of VC decrease as the total carbon of alloy decreases in VC-Co alloy. The morphology of VC is near spherical and does not change with carbon content. As the total carbon of alloy decreases in the case of NbC-Co alloy, the content of combined carbon of NbC decreases, the average grain size increases. There is shape transition from cubic to octahedron consisting of {111} planes through tetradecahedron because {111} planes start to develope at the corner of cuvic due to lower surface energy of {111} planes. There has been few studies on the shape transition of NbC particles.
The size of NbC of which {111} face is developed in low carbon alloy is much larger than NbC cubic grain grown in high carbon alloy.

목차 (Table of Contents)

• 목차 = i
• I. 서론 = 1
• 1. 서언 = 1
• 2. 연구 배경 = 2
• 3. 본 논문의 구성 = 8
• 참고문헌 = 9
• II. 이론적 고찰 = 12
• 1. WC 및 Co의 특성 = 12
• 2. WC-Co 상태도와 Co 결합상 및 η 상의 특성 = 17
• 3. WC-Co 초경합금의 기계적 성질 = 25
• 1) 초경합금의 경도 = 25
• 2) 초경합금의 항절력 = 30
• 3) Palmqvist 인성 = 35
• 참고문헌 = 40
• III. WC-Co계 초경합금 중 총 탄소량이 결합상, 탄화물 및 합금강도에 미치는 영향. = 45
• 1. 서론 = 45
• 2. 실험방법 = 48
• 3. 실험결과 및 고찰 = 52
• 1) 합금의 총 탄소량에 따른 Co 결합상 조성과 자기포화도 = 52
• 2) 함금의 Co 량에 따른 건전상역의 범위 = 65
• 3) 합금의 총 탄소량에 따른 탄화물의 입도, 입도분포 및 합금의 경도 = 70
• 4) 합금의 총 탄소량에 따른 항절력과 파괴인성 = 75
• 4. 결언 = 85
• 참고문헌 = 87
• IV. NbC-Co 및 VC-Co 초경합금의 총 탄소량이 결합상 및 탄화물의 특성에 미치는 영향 = 89
• 1. 서론 = 89
• 2. 실험 방법 = 91
• 3. 실험결과 = 94
• 1) 합금의 총 탄소량에 따른 Co 결합상 조성과 자기포화도 = 94
• 2) 합금의 총 탄소량에 따른 탄화물상의 결합탄소량 변화 = 100
• 3) 합금의 총 탄소량에 따른 탄화물 입도 및 형상의 변화 = 100
• 4. 고찰 = 109
• 5. 결언 = 114
• 참고문헌 = 115
• V. TiC-Mo_(2)C-(Co+Ni)계 서메트에서 총 탄소량, (Ni/Co)비가 결합상의 조성에 미치는 영향 = 116
• 1. 서론 = 116
• 2. 실험방법 = 118
• 3. 실험 결과 및 고찰 = 119
• 1) 합금의 총 탄소량에 따른 결합상의 조성과 자기포화도 = 119
• 2) 결합상의 종류와 합금의 총 탄소량에 따른 조직과 경도 = 127
• 4. 결언 = 131
• 참고문헌 = 132
• VI. 미립 WC를 사용한 초경합금의 비정상 입자성장과 η 상 = 134
• 1. 서론 = 134
• 2. 실험방법 = 135
• 3. 실험결과 및 고찰 = 137
• 1) 원료탄화물 중 조대입자와 비정상 성장입자의 관계 = 137
• 2) η 상과 비정상 성장 입자의 관계 = 142
• 3) η 상의 형상 및 조성. = 144
• 4. 결언 = 154
• 참고문헌 = 155
• VII. 초경합금 중 WC 입자성장 억제와 WC의 형상 = 156
• 1. 서언 = 156
• 2. 실험방법 = 157
• 3. 실험결과 및 고찰 = 158
• 1) 타 탄화물의 WC에 대한 입자성장 억제 효과 = 158
• 2) 타 탄화물의 첨가에 의한 비정상 성장입자의 형상 변화. = 164
• 4. 결언 = 171
• 참고문헌 = 172
• VIII. 총괄 = 173
• (Abstract) = 177