Shot Peening dan Sputtering TiN pada AISI 304 untuk Meningkatkan Umur Fatik dalam Media Korosif sebagai Biomaterial Alternatif

BAMBANG HARI PRIYAMBODO, Dr. Ir. Viktor Malau, DEA.; Dr. Eng. Priyo Tri Iswanto, ST., M.Eng.

2020 | Disertasi | DOKTOR TEKNIK MESIN

AISI 304 merupakan salah satu material baja tahan karat dengan harga relatif murah serta banyak ditemukan di pasaran dibandingkan material lainnya yang digunakan untuk bahan biomaterial saat ini. Namun demikian, sifat mekanis dan ketahanan korosinya perlu ditingkakan minimal mendekati sifat baja tahan karat yang digunakan untuk biomaterial,sebagai contoh AISI 316L maupun logam paduan berbasis cobalt dan titanium. Shot peening dan sputtering adalah metode perlakuan permukaan yang digunakan untuk meningkatkan sifat mekanis dan ketahanan korosi pada AISI 304. Shot peening merupakan proses perlakuan permukaan dengan menembakkan bola-bola baja kecepatan tinggi pada permukaan logam yang dapat menimbulkan kerapatan dislokasi pada batas butir sehingga bahan menjadi lebih keras dan tahan korosi. Sputtering adalah proses penyisipan atom target (bahan pelapis) pada permukaan substrat. Deposisi lapisan tipis titanium nitrida (TiN) memiliki sifat keras, tahan korosi, tahan abrasi, tahan suhu tinggi, koefisien gesek rendah, dan biokompatibel. Dalam penelitian ini dilakukan gabungan shot peening dan sputtering pada permukaan AISI 304, dimana keunggulan dari kedua metode tersebut akan saling melengkapi dan menghasilkan sifat baru yang lebih unggul. Metode penelitian tentang shot peening dilakukan dengan cara menembakkan bola-bola baja dengan variasi ukuran bola baja diameter 0,2; 0,5 dan 0,8 mm selama 20 menit. Tekanan kompresor diatur dengan variasi sebesar 7, 8, dan 9 bar. Kekerasan bola-bola baja yang dipakai untuk proses shot peening sebesar 40-50 HRC. Jarak tembak antara nosel dengan spesimen sebesar 10 cm. Proses sputtering TiN dilakukan dengan mengatur parameter kuat arus sebesar 25-30 mA, tegangan 2,5-3 KV, jarak antara substrat dan target 10 mm, variasi lama sputtering 30, 60, 90, 120, dan 150 menit, serta variasi komposisi gas Nitrogen 10%, 20% dan 30%. Parameter hasil pengujian korosi terbaik dari metode shot peening dan sputtering TiN digunakan sebagai parameter gabungan shot peening dan sputtering TiN. Penelitian sifat mekanis, korosi dan laju perambatan retak fatik telah dilakukan. Hasil penelitian menunjukkan bahwa kekerasan, laju korosi dan laju perambatan retak fatik AISI 304 dapat diperbaiki. Gabungan shot peening dan sputtering TiN dapat meningkatkan kekerasan permukaan AISI 304 sebesar 496 VHN atau sekitar 206% lebih tinggi dibandingkan spesimen non treatment. Nilai laju korosi spesimen gabungan shot peening dan sputtering TiN sebesar 0,057 mpy dan terjadi penurunan sekitar 79% dari spesimen non treatment. Umur fatik spesimen gabungan shot peening dan sputtering TiN meningkat sekitar 27% dari spesimen non treatment, yang ditunjukkan dengan peningkatan jumlah siklus pembebanan.

AISI 304 is stainless steel material at a relatively cheap price and is more commonly found on the market compared to other materials used for biomaterials today. However, the mechanical properties and corrosion resistance need to be increased at least close to the nature of stainless steel used for biomaterials, for example, AISI 316L or cobalt and titanium-based alloys. Shot peening and sputtering are surface treatment methods used to improve mechanical properties and corrosion resistance on AISI 304. Shot peening is a surface treatment process by shooting high-speed steel balls on metal surfaces that can cause dislocation densities at grain boundaries so that material becomes harder and corrosion-resistant. Sputtering is the process of inserting a target atom (coating material) on the surface of a substrate. Titanium nitride (TiN) thin film deposition is hard, corrosion-resistant, abrasion-resistant, high temperature resistant, low friction coefficient, and biocompatible. In this study, a combination of shot peening and sputtering was carried out on the surface of AISI 304, where the advantages of the two methods would complement each other and produce new properties that were superior. The research method of shot peening was done by shooting steel balls with variations in the size of steel balls with a diameter of 0.2; 0.5 and 0.8 mm for 20 minutes. Compressor pressure was regulated by variations of 7, 8 and 9 bar. The hardness of the steel balls used for the shot peening process is 40-50 HRC. The shooting distance between the nozzle and the specimen was 10 cm. The TiN sputtering process was carried out by adjusting the current strength parameters of 25-30 mA, the voltage of 2.5-3 kV, the distance between the substrate and the target of 10 mm, the sputtering duration variation of 30, 60, 90, 120, and 150 minutes, as well as variations in gas composition 10%, 20%, and 30% nitrogen. The best corrosion test parameter results from the shot peening and sputtering TiN methods were used as the combined parameters of shot peening and TiN sputtering. Research on mechanical properties, corrosion and fatigue crack propagation rates have been done. The results showed that the hardness, corrosion rate and propagation rate of AISI 304 fatigue cracks could be improved. The combination of shot peening and sputtering TiN can increase the surface hardness of AISI 304 by 496 VHN or about 206% higher than non-treatment specimens. The corrosion rate of the combination shot peening and sputtering TiN specimens was 0.057 mpy and there was a decrease of about 79% of the non-treatment specimens. The fatigue life of the combination shot peening and sputtering TiN specimens increased by about 27% of the non-treatment specimen, as indicated by an increase in the number of loading cycles.

Kata Kunci : AISI 304, shot peening, sputtering TiN, laju perambatan retak fatik.