Sains Malaysiana 42(12)(2013):
1769–1773
Phase
Transformation Temperatures (PPTs) and Microstructure of
Moulded
NiTi Alloy Using a Water Soluble Binder System
(Suhu Perubahan Fasa dan Mikrostruktur Aloi NiTi Teracuan
Menggunakan Sistem Bahan Pengikat Larut Air)
MUHAMMAD HUSSAIN ISMAIL1*, MARTIN BRAM2, ANA PAULA CYSNE BARBOSA2, MANUEL KÖHL2, HYWEL A. DAVIES3& IAIN TODD3
1Faculty of Mechanical Engineering, Universiti
Teknologi MARA (UiTM)
40450 Shah Alam, Selangor, Malaysia
2Institute of Energy Research (IEF-1), Jülich,
52425, Jülich, Germany
3Department of Material Science & Engineering, University of Sheffield
Sir Robert Hadfield Building, Mappin
Street, S 1 3J Sheffield, United Kingdom
Diserahkan: 25 April 2012/Diterima: 31 Mei 2012
ABSTRACT
In this work, the effects of backbone polymer in the binder system
mixed with pre-alloyed NiTi powder, on impurity contents, phase transformation
temperatures and microstructures were investigated. A spherical gas-atomised
pre-alloyed NiTi powder (50.3 at. %Ni) with a mean particle size of less than
22 μm and powder loading of
69.5 vol. % was used. The binder consisted of a water soluble binder system,
mainly polyethylene glycol (PEG), with two different backbone binders,
namely polyethylene 520 (PE 520) and poly-methyl- methacrylate (PMMA).
The latter was used in the form of a powder and as an emulsion. Green parts
were prepared by warm-press the feedstock into a cylindrical shape. The samples
were then leached in warm water, thermally debound in Argon and finally, vacuum
sintered at 1240°C for 10 h. The experimental results indicate that the oxygen
content in the as-sintered condition increased to almost double than that of
the powder state (from 0.08 to 0.14 - 0.16 wt. %) and the carbon increased by
one third to half (from 0.06 to 0.08 - 0.09 wt. %). This consequently resulted
in a shift of the phase transformation temperature to lower values and
consequently broadened the reversible austenite to martensite transformation.
The uptake of oxygen and carbon during the process led to the formation of the
well-known Ti4Ni2Ox and TiC precipitate
phases which were evident from grey-scale images of back-scattered SEM.
Keywords: Metal injection moulding (MIM); NiTi alloy; phase
transformation temperatures (PTTs); pseudo-elasticity; shape memory
ABSTRAK
Dalam kajian ini, kesan polimer sekunder di dalam campuran bahan
suapan pengacuan suntikan logam yang terdiri daripada serbuk logam pra-aloi
NiTi terhadap kandungan bendasing, suhu penjelmaan fasa dan mikrostruktur yang
terbentuk telah dikaji. Serbuk logam NiTi yang digunakan mempunyai komposisi
kimia 50.3 at. %Ni dengan saiz purata serbuk kurang daripada 22 μm dan telah dihasilkan secara pembutiran gas.
Sebanyak 3 formulasi bahan suapan telah dikaji dengan menggunakan isi padu
serbuk yang sama (69.5 vol. %). Komposisi bahan
pengikat dalam bahan suapan adalah terdiri daripada polimer primer yang sama iaitu poli-etilena-glikol (PEG) dan polimer sekunder
pula terdiri daripada polietilena (PE 520) dan poli-metil-meta-akrilik (PMMA).
Untuk kes PMMA, 2 bentuk telah digunakan, iaitu pertamanya dalam
bentuk serbuk dan keduanya dalam bentuk emulsi. Bahan suapan
yang dihasilkan seterusnya diproses menjadi bentuk silinder dengan menggunakan
kaedah padatan hangat. Sampel kemudiannya direndam di
dalam air yang hangat untuk mengeluarkan bahan pengikat primer, iaitu PEG. Sampel kemudiannya dikeringkan sebelum dibawa ke relau vakum untuk proses
penyahikatan terma dan persinteran. Proses penyahikatan terma dijalankan dalam
persekitaran Argon dan diakhiri dengan persinteran dalam vakum pada suhu 1240°C
selama 10 jam. Hasil uji kaji menunjukkan kandungan oksigen dalam sampel yang
disinter meningkat hampir dua kali ganda berbanding dalam keadaan serbuk
(daripada 0.08 ke 0.14-0.16 wt. %), manakala kandungan karbon pula meningkat
antara separuh ke satu pertiga (daripada 0.06 ke 0.08-0.09 wt. %). Keadaan ini seterusnya menyebabkan pengurangan pada suhu penjelmaan
fasa dan meluaskan julat perubahan suhu boleh balik daripada fasa austenite ke
martensite. Peningkatan kandungan oksigen dan karbon
pada sampel tersinter juga menunjukkan wujudnya fasa sekunder seperti Ti4Ni2Ox dan
TiC yang dibuktikan daripada perbezaan warna pada setiap fasa pada gambarajah SEM dan
seterusnya melalui bacaan EDX.
Kata kunci: Aloi NiTi;
memori bentuk; pengacuan suntikan logam; pseudo-keanjalan; suhu penjelmaan fasa
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*Pengarang untuk surat-menyurat; email: hussain305@salam.uitm.edu.my
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