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Chapter 6. Metal Matrix Composites 6. Metal Matrix Composites MMC system : 1. Boron/aluminum 2. Carbon/aluminum 3. Al2O3/Al and Al2O3/Mg 4. SiC/Al 5. Eutectic or in situ composites (really a subclass of MMCs) Functional Metal Matrix Composites Advantage of MMC High specific strength/ modulus Improvement of Heat Resistance Low Thermal Expansion/heat Conductivity Functional Gradient Property Why do we need to fabricate MMC ? Current development and Aim of MMC Component Technology 연구내용 개발현황 및 문제점 원천기술 목표 자동차 부품 주철→Al→Mg으로 경량화 내열Mg MMC개발 Cylinder block Mg의 경우 Creep, 열피로 강도 부족 creep rate~1.5х10-8/s, 항복강도~200MPa, 고성능 엔진에 따라 고기능 재료 요구 감쇠특성 ~1.0×10-2, 탄성계수 ~50GPa Ti → Ti6Al4V → Ti6Al7Nb → Ti HAp코팅 경사기능 Ti/HAp MMC개발 바이오 부품 강도부족 Implant 생체적합성 부족 (골성장 방해, 인체유독성) 전자 부품 packaging 현 Ti합금 수준의 강도확보 in-vivo test 합격목표 Package : Kovar(Fe-Ni),CuW,CuMo 고전도·저팽창 경량 Al/SiCp 개발 Substrate : Alumina, Beryllia, SiC, AlN 열전도:~170W/mK, CTE:~8×10-6/K, 전도성 / 팽창 / 경량의 조화재료 요구 Density:~3g/cm3 인용: 부산대기능성첨단금속복합재료연구팀자료 MMC for Airplane, Wind power, Yacht 인용: 부산대기능성첨단금속복합재료연구팀자료 Space trip starts from Development of Composites 인용: 부산대기능성첨단금속복합재료연구팀자료 How is car engine operating? –DVD 4 cyle enine : Intake, compression, explosion, exhaustion? 인용: 부산대 기능성첨단금속복합재료 연구팀자료 MMC Application for Engine 포르쉐 911 모델에 사용되 는 실린더 블록은 복합재료 를 사용하여 만들었다. 자동차에 이용되는 엔진 피스톤 부분에 복합재료가 사용된다. 인용: 부산대기능성첨단금속복합재료연구팀자료 Design of Automotive engine cylinder bore high wear resistance, h. strength, h. compressive strength, 인용: 부산대기능성첨단금속복합재료연구팀자료 6.1 Fabrication of MMCs - A simple classification of metal matrix composite fabrication methods 1. Solid state fabrication techniques 2. Liquid state fabrication techniques 3. In situ fabrication techniques 6.1 Fabrication of MMCs - In solid state fabrication and liquid state fabrication, it may be necessary to coat the fiber or prepare fiber/matrix performs for later consolidation and/or secondary fabrication. → Fiber surfaces may be coated with suitable materials to (a) improve wettability and adhesion (b) prevent any adverse chemical interaction between the fiber and matrix at elevated temperatures 6.1.1 Solid State Fabrication - Boron fiber and aluminum foils, resin-based fugitive binder Functional MMC fabrication Technology1 Preform Fabrication MMC 구조설계 및 해석 Problem강화재의 편석및 예비성형체의 변형 부피분율조정및 정밀 형상 제조의 어려움 Solution Binder slurry additives 조절 Rapid prototype, P/M 기술 도입 Silica colloid inorganic binder Mutual repulsion 문제점 기능성 MMC특성 평가기술 미흡 열·기계적 변형/FGM 해석모델 미흡 MMC특성평가 제어기술 확립 해결 방안 열적·기계적 변형 / FGM 모델제시 Attraction Minimization of preform deformation Cationic starch organic binder Flocking effect between inorganic binder and reinforcements Graphite + Whisker Cationic polyacrylamide Minimization of anisotropic distribution of Flocculation reinforcements Dodecylbenzenesulfonate Removal of gas pore Graphite + Whisker + Starch Preform 제조시의 slurry additives의 영향 경사기능 복합재료의 구조해석 예 6.1.1 Solid State Fabrication - Powder metallurgy techniques : discontinuous fibers or whiskers → Matrix metal powder and fibers are mixed and then pressed to consolidate → Sintering 6.1.1 Solid State Fabrication - Plasma spray, CVD or PVD of matrix material onto properly laid-up fibers followed by some kind of consolidation technique(vacuum hot press, hot isostatic pressing) 1. Plasma spray : very versatile technique of joining any two dissimilar materials 2. Low-Pressure Plasma Deposition(LPPD) : very flexible method of producing composites with different volume fractions of reinforcement and matrix phase distribution, bonding, and so on 6.1.1 Solid State Fabrication Good bonding is not obtained -> Roll bonding and explosive bonding are also used to join two dissimilar metals. Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998) 6.1.2 Liquid State Fabrication - All methods in this category involve liquid metal (matrix) infiltration of fibers or fiber preforms. → The liquid penetration around the fiber bundles can occur by capillary action, vacuum infiltration, or pressure infiltration. - Squeeze Casting : The application of high pressures to the liquid metal during solidification. 6.1.2 Liquid State Fabrication → Pore free, fine grained aluminum alloy components having superior properties. 6.1.2 Liquid State Fabrication 1. A porous fiber preform is inserted into the die 2. Molten metal is poured into the preheated die 3. The applied pressure(70-100MPa)makes the molten aluminum penetrate the fiber preform and bond the fibers. 기능성금속복합재료의 제조기술 2 Squeeze Infiltration 공정 문제점 해결 방안 수축공, 기공 등의 주조결함 발생 균열발생, 이형결함 Preform 예열 및 용탕온도 제어 가압력 및 가압속도 제어 부분복합화 Al MMC piston의 제조공정상 문제 용탕응고유동해석 부분가압에 따른 응고경계조건 변화 문제점 Preform 삽입에 따른 응고유동 변화 해결 방안 다공성 응고유동 모델 확립 응고해석 S/W 개발 단일소재 부품의 용탕응고유동 해석 사례 (부 산대) 인용: 부산대기능성첨단금속복합재료연구팀자료 전자 패키징 재료를 위한 금속 복합재료의 응용 (a)침투방법에 의하여 만들어진 70vol%SiCp/Al 금속복합재료의 미세구조 (b) 전자패키징 재료의 응용 인용: 부산대기능성첨단금속복합재료연구팀자료 6.1.3 In Situ Fabrication Techniques - Controlled unidirectional solidification of a eutectic alloy can result in a two-phase microstructure with one of the phases, present in lamellar or fiber form, distributed in the matrix At low solidification rates -> The TaC fibers are square in cross section At higher solidification rates -> Blades of TaC form The number of fibers per square centimeter also increased with increasing solidification rate 6.1.2 Liquid State Fabrication Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998) 6.2 Interface in Metal Matrix Composites - In MMCs, as in other composites, we can have mechanical bonding as well as chemical bonding. 6.2.1 Mechanical Bonding Mechanical bonding restores the strength to levels Achieved in reaction bonding Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998) 6.2.2 Chemical Bonding - Some controlled amount of reaction at the interface may even be desirable for obtaining strong bonding between the fiber and the matrix. - Too thick an interaction zone, however, will adversely affect the composite properties. - Improvements in interfacial bonding in MMCs are frequently obtained by two methods : Fiber surface treatment, Matrix modification 6.2.2 Chemical Bonding Fiber Surface Treatment (a) To improve wettability and adhesion (b) To prevent any adverse chemical interaction between the fiber and the matrix at elevated temperature Krishan K. Chawla, Composite materials science and engineering, Springer-Verlag, (1998) 6.2.2 Chemical Bonding In the case of carbon fibers in aluminum, poor wettability is a major problem. - The idea is to alter the matrix composition in such a way that dopants would react with the fiber. - In a controlled manner to give a thin fiber surface layer that will be wetted by the liquid matrix alloy.