WC-Co 및 TiC-Ni계 복합재료의 평면변형 파괴인성에 관한 연구

Abstract

본연구에서는 WC-Co 및 TiC-Ni계 복합재료의 탄화물 입도, 결합상의 평균자유 행로, 합금원소 및 탄화물의 체적분율의 변화에 따른 평면변형 파괴인성을 방전가공에 의해 노?「? 부여한 SENB시편을 사용하여 측정하였다. 또한 복합재료인 WC-Co 및 TiC-Ni합금의 기계적 성질을 조사하기 위하여 경도, 항절력, 충격강도 및 Palmqvist 균열저항도 측정하였으며 얻어진 결론은 다음과 같다.

1) 항절력 시험결과 항절력은 결합상의 진평균 자유행로의 임계값에서 최대 값을 갖는다.

2) 충격강도는 결합상의 양에 따라 증가하나 합금의 탄화물 입도에 따른 영향은 거의 없다.

3) Palmqvist 균열저항 시험으로 부터 얻어진 결과는 10³/W=AH-B이며 여기서 W는 균열저항 계수, H는 비커스 경도이며 상수 A,B는 WC-Co계 합금의 경우는 각각 0.0175, 14.7 값을 갖으며 TiC-Ni계 합금의 경우는 각각 0.0175, 16.6 값을 갖는다. 이 관계식은 초겅합금의 연구와 품질관리에 유용한 식이 될 수 있다.

4) 복합재료의 평면변형 파괴인성(K??)은 현미경 조직인자 중 특히 결함상의 진평균 자유행로와 탄화물의 분리정도(1-C)에 의존하며 파괴인성은 복합재료의 경도 증가에 따라 직선적으로 감소한다. 선형탄성 파괴역학에 근거로 부터 계산된 임계변형에너지 해방률 G??는 진평균 자유행로의 증가와 더불어 직선적으로 증가한다.

The plane strain fracture toughness(K??) of WC-Co and TiC-Ni composites was measured as a function of carbide grain size, mean free path of binder, alloying elements and volume fraction of carbide using single-edge notched beam(SENB) specimens of whigh notch formed by electron discharge machining(EDM). To evaluate the mechanical behavior of WC-Co and TiC-Ni composites, measurements of hardness, transverse rupture strength(TRS), impact strength and Palmqvist crack resistance were employed.

The results obtained are as foliows:

1) In transverse rupture test, it has been found that TRS reaches a maximum value at the critical value of true mean free path of binder.

2) Impact strength increased with the increase of binder content, but the effect of carbide grain size was relatively small.

3) The empirical relationship between Palmqvist test crack resistance(W) and Vicker's hardness(H?) is as follows :

10³/W = AH - B

where constants A and B are 0.0175 and 14.7 respectively for WC-Co base composites and 0.0175 and 16.6 for TiC-Ni base composites.

It is considered that this relationship will be very useful for bath the development of cemented carbides and quality control is the production line.

4) The plane strain fracture toughness(K??) of composites depends on the microstructural parameters, particularly on the true mean free path(λ) of binder content and decree of separation of carbide grains(1-C). The fracture toughness decreased linearly with the increasing hardness of composites.

The critical strain energy release rate(G??) increased linearly with the increase of the true mean free path.

The plane strain fracture toughness(K??) of WC-Co and TiC-Ni composites was measured as a function of carbide grain size, mean free path of binder, alloying elements and volume fraction of carbide using single-edge notched beam(SENB) specimens of whigh notch formed by electron discharge machining(EDM). To evaluate the mechanical behavior of WC-Co and TiC-Ni composites, measurements of hardness, transverse rupture strength(TRS), impact strength and Palmqvist crack resistance were employed.

The results obtained are as foliows:

1) In transverse rupture test, it has been found that TRS reaches a maximum value at the critical value of true mean free path of binder.

2) Impact strength increased with the increase of binder content, but the effect of carbide grain size was relatively small.

3) The empirical relationship between Palmqvist test crack resistance(W) and Vicker's hardness(H?) is as follows :

10³/W = AH - B

where constants A and B are 0.0175 and 14.7 respectively for WC-Co base composites and 0.0175 and 16.6 for TiC-Ni base composites.

It is considered that this relationship will be very useful for bath the development of cemented carbides and quality control is the production line.

4) The plane strain fracture toughness(K??) of composites depends on the microstructural parameters, particularly on the true mean free path(λ) of binder content and decree of separation of carbide grains(1-C). The fracture toughness decreased linearly with the increasing hardness of composites.

The critical strain energy release rate(G??) increased linearly with the increase of the true mean free path.