Keramik merupakan salah satu material teknik yang baru dikembangkan, mempunyai banyak keunggulan diantaranya: titik cair tinggi, tahan terhadap beban tekan, tahan gesekan, tahan korosi, densitas relatif rendah, koefisien muai panas rendah, konduktifitas panas dan listrik rendah. Namun demikian untuk aplikasi di bidang teknik keramik mempunyai kelemahan yaitu bersifat getas dan fracture toughness-nya rendah. Ceramic Matrix Composites (CMC) merupakan salah satu solusi untuk mengurangi kelemahan tersebut. Penelitian ini bertujuan untuk mengetahui pengaruh penambahan partikel nikel terhadap sifat fisis dan mekanis alumina yang mengandung 20% berat silika. Alumina (Al2O3) yang mengandung 20 % berat silika (SiO2) yang diperkuat dengan 0, 3, 6, 9, 12 dan 15 % volume partikel nikel (Ni) telah dibuat dengan metode pressureless sintering, masing-masing komposisi di-mixing dengan proses basah (dengan alkohol) selama 5 jam, dikeringkan selama 24 jam pada temperatur kamar dan dilanjutkan dengan mixing kering selama 5 jam. Pembuatan spesimen berbentuk silindris (diameter d=15mm, tebal t=5mm), balok (panjang L=50mm, lebar B=7mm, tinggi W=8mm) dan balok yang diberi takikan 45o sebagai retak awal dilakukan dengan uniaxial-pressing dengan tekanan 120 MPa. Spesimen silindris disinter di lingkungan argon dengan laju pemanasan 3 oC/menit sampai temperatur 800 oC dan ditahan selama 30 menit, kemudian dinaikkan dengan laju pemanasan 5 oC/menit hingga temperatur sinter dan ditahan 60 menit. Temperatur sinter bervariasi 1400, 1425 dan 1450 oC. Pendinginan dilakukan di dalam furnace dengan cara mematikan power ke furnace. Hasil pengujian menunjukkan bahwa densitas tertinggi diperoleh pada spesimen dengan temperatur sinter 1425 oC yang dihitung dengan menggunakan teori Archimedes. Pengujian kekerasan Vickers dengan beban 153,2 N menunjukkan penurunan kekerasan bahan dari 824 MPa (komposit dengan 0% volume Ni) menjadi 540 MPa (komposit dengan 15% volume Ni). Fracture toughness yang diukur dengan metode Single Edge Notched Beam meningkat dari 0,76 MPa.m1/2 (komposit dengan 0% volume Ni) menjadi 1,03 MPa.m1/2 (komposit dengan 12% volume Ni). Four-point bending test digunakan untuk menguji kekuatan bending atau óMOR dan memberikan peningkatan hasil dari 32,0 MPa (komposit dengan 0% volume Ni) menjadi 37,0 MPa (komposit dengan 9 dan 12% volume Ni). Peningkatan fracture toughness terjadi dengan mekanisme crack deflection, crack bridging dan crack branching.

Ceramics are materials which generally have excellent properties such as high melting point, high hardness, good wear resistance, good corrosion resistance, relatively low density, low thermal expansion, relatively low thermal and electrical conductivity. Ceramics however have limitation in engineering applications because of their brittleness and low fracture toughness. Introduction ductile metal as reinforcement into ceramic matrix has become a way to overcome such drawback and increase fracture toughness since the ductile metal may reduce crack propagation. Alumina is an interesting ceramic material for developing ceramic-metal composites. The present study aims to investigate the effect of nickel particles addition on physical and mechanical properties of alumina. Alumina (containing 20 % weight SiO2) as a matrix was reinforced with (0, 3, 6, 9, 12, and 15 % volume) nickel. Each composition was wet-mixed in alcohol for 5 hours. The mixture was then dried in air for 24 hours and is followed by dry-mixed for 5 hours. Three different dimensions of green samples i.e. cylindrical with 15 mm diameter, square (length L = 50 mm, width B = 7 mm and thickness W = 8 mm) and square (length L = 50 mm, width B = 7 mm and thickness W = 8 mm) with an V-notch were prepared by using uni-axial steel die with a pressure of 120 MPa. The cylindrical samples were pressureless sintered in a horizontal tube furnace with a heating rate of 3oC/minute up to 800oC and it was hold for 30 minute. The temperature was then increased again from 800oC to a sintering temperature (1400oC, 1425oC and 1450oC) with a heating rate of 5oC/minute and a holding time for 60 minutes at that temperature. The furnace was cooled from the sintering temperature by switched the furnace power off. Sintering at 1425oC was found to be the optimum temperature to get highest density of samples and this temperature was chosen to produce samples for mechanical testing. Hardness of the samples was measured using Vickers hardness test with a load of 153.2 N and the results show that the Vickers hardness decreases from 824 MPa for composites with 0% volume nickel to 540 MPa for composites with 15 %volume nickel. This decrease of Vickers hardness is due to nickel having lower Vickers hardness than that of alumina matrix. Single-Edge Notched Beam method was used for fracture toughness measurement. The fracture toughness slightly increases from 0.76 MPa.mo.5 for composites with 0% volume nickel to 1.03 MPa.mo.5 for composites with 12 %volume nickel. The increase of fracture toughness occurs due to crack deflection, crack bridging and crack branching mechanisms. Strength of the samples was measured using four point bending test. The bending strength increases with increasing nickel content up to 12 % volume. Optical microscopy and SEM were used to observe the microstructures and fracture surface of samples.

Kata Kunci : CMC,Alumina (Al2O3) S1 O2,Nikel,Presureless Sintering, alumina, silica, nickel, pressureless sintering, fracture toughness, density.