Formation Of Single Phase Niti Shape Memory Alloy Via Solid State Processing In Reducing Environment

Perkembangan pesat aplikasi terutamanya dalam bidang perubatan dan kejuruteraan menuntut kepada pembangunan NiTi berstruktur nobel yang mana memerlukan teknik pemprosesan alternatif, selain dari teknik konvensional secara peleburan. Sintesis berkeadaan pejal merupakan teknik pemprosesan alternatif untuk menghasilkan NiTi berstruktur nobel seperti struktur poros dan juga struktur nobel yang lain. Sementara sifat memori bentuk NiTi yang unik adalah satu kelebihan, tiada tercatat percubaan yang berjaya dalam menghasilkan fasa aloi tunggal NiTi yang mempamerkan transformasi martensitik yang baik. Kebanyakan produk yang terhasil melalui kaedah sintesis keadaan pejal mempunyai struktur mikro yang kompleks melibatkan pembentukan fasa lain seperti Ti2Ni dan TiNi3. Fasa-fasa ini tidak mempunyai transformasi martensitik, justeru menjejaskan sifat memori bentuknya. Selain itu, pembentukan oksida boleh menghalang kepada pembentukan fasa aloi tunggal NiTi. Oleh yang demikian, kajian ini bertujuan untuk mengkaji keadaan yang membolehkan terbentuknya fasa aloi tunggal NiTi yang mempunyai sifat transformasi martensitic yang optimum dan juga mengenalpasti rintangan kepada pembentukan fasa aloi tunggal NiTi ini. Dalam kajian ini, serbuk campuran Ni-Ti dan Ni-TiH2 disintesiskan dalam aliran argon dan persekitaran terkawal menggunakan serbuk CaH2 dan MgH2 sebagai agen penurunan in-situ. Pelbagai parameter seperti suhu pensinteran, masa, komposisi, dan rawatan haba pasca pensinteran digunakan untuk mengkaji kesan kepada pembentukan fasa aloi, sifat martensitik, perubahan ingatan bentuk dan juga sifat mekanikalnya. Sintesis menggunakan Ni-Ti tidak menghasilkan fasa aloi tunggal NiTi, justeru tiada nilai entalpi yang menjadi ukuran untuk sifat martensitiknya. Penggunaan serbuk TiH2 menggantikan serbuk Ti berjaya meningkatkan jumlah peratusan fasa aloi tunggal NiTi dengan nilai entalpi iaitu ≤13 J/g. Walaubagaimanapun, nilainya agak kecil jika dibandingkan dengan nilai ideal untuk NiTi. Puncanya adalah disebabkan oleh pengaruh pengoksidaan yang menghalang pembentukan fasa aloi tunggal NiTi. Sintesis NiTi menggunakan serbuk Ni-TiH2 dan CaH2 sebagai agen penurunan insitu, berjaya menghasilkan fasa aloi tunggal NiTi dengan nilai entalpi sebanyak 25 hingga 26 J/g, iaitu bersamaan dengan nilai entalpi yang ideal untuk NiTi. Analisis pada permukaan spesimen menunjukkan ada perubahan yang ketara dalam mengurangkan lapisan oksida yang terbentuk, justeru meminimumkan kesan terhadap ketidakseimbangan unsur-unsur Ni-Ti untuk tindakbalas pembentukan fasa aloi tunggal NiTi. Ini menjadikan sintesis melalui persekitaran tanpa oksigen membolehkan terbentuknya fasa aloi tunggal NiTi. Selain dari pertimbangan termodinamik yang kerap dibincangkan menjadi faktor terhalang pembentukan fasa aloi tunggal NiTi, penyelidikan ini berupaya mewujudkan fakta bahawa pengoksidaan memberikan kesan ketara kepada pembentukan fasa aloi tunggal NiTi disintesiskan dalam keadaan pejal. ________________________________________________________________________________________________________________________ The fast growing application especially in medical and engineering fields demands the development of novel-structured NiTi which requires an alternative processing technique, other than the conventional melt-casting method. Solid state synthesis is an alternative processing technique that has been attempted for producing novelstructured NiTi such as porous NiTi and other novel forms. Whilst shape memory effect is a unique advantage of NiTi shape memory alloy like, no successful attempt so far to produce single phase NiTi with good transformation. NiTi produced via solid state synthesis have complex microstructures involving multiple phases of Ti2Ni and TiNi3. These phases do not exhibit martensitic transformation and jeopardise the shape memory behaviour of NiTi. Apart from that, the formation of oxides may hinder the formation of single phase NiTi. Therefore, this research examines the processing conditions that produce single phase NiTi with optimum transformation behaviour and also identifies the possible obstacles for forming single phase NiTi. This study synthesised Ni-Ti and Ni-TiH2 powder mixtures in flowing argon and reducing environment using CaH2 and MgH2 powder as the in situ reducing agent. Several effects of parameters such as sintering temperature, time, composition, and post-sintering were studied and a systematic comparative investigation was performed on phase formation, transformation behaviour, shape memory effect, and deformation behaviour of the sintered specimen. Elemental powder sintering of Ni-Ti did not result in single phase NiTi and no distinct peaks of martensitic transformation were observed on the sintered specimens. The use of TiH2 to replace Ti increased the volume fraction of NiTi and displayed martensitic transformation peaks, albeit with low transformation heat (≤13 J/g) revealing that oxidation is an active obstacle in producing single phase NiTi. Synthesis of Ni-TiH2 in reducing the environment, especially the use of CaH2 as an in situ reducing agent, resulted in the formation of single phase NiTi with enthalpy change of ~25-26 J/g, similar to melt-cast NiTi alloys. The surface analysis showed a significant reduction in oxide formation, thus minimising the effects on balanced composition between Ni and Ti. This reflects that an oxygen-free environment allows unhindered Ni-Ti reaction, which leads to the formation of single-phase NiTi. This work established the fact that, other than the thermodynamic considerations often being discussed in similar work as obstacles to single phase formation, oxidation appears to have profound effects on single phase formation in NiTi synthesized in solid state

A study of CaH2 effectiveness as oxidation prevention in solid state sintering of single phase NiTi alloy

This research aims to study the conditions that may produce single phase NiTi for desirable shape memory effect under solid state by suppressing the oxide levels using CaH2 as in-situ reducing agent. A systematic comparative investigation was made on phase formation and their transformation behavior. Phase formation analysis was carried out using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscope (EDS) and X-Ray Diffractometer (XRD). The transformation behaviour was studied by means of Differential Scanning Calorimetry (DSC) measurements. Thermomechanical analysis was conducted using Thermomechanical Analyzer (TMA). The study revealed that single phase NiTi was successfully formed from Ni-TiH2 specimen sintered at 930°C for 3 h under CaH2 reducing environment with good enthalpy change of ΔHA-M = 26 J g-1 and ΔHM-A = 25.5 J g-1 upon cooling and heating, respectively. However, the recovery strain reaches 0.75% at maximum 8 N applied load which is still below than the reported bulk NiTi

Effect of acceptor impurity (Cu and Al) in Zn4Sb3 thermoelectric materials via hotisostatic pressing (HIP) method

This project investigates the influence of dopants use via hot-isostatic pressing (HIP) sintering technique on thermoelectric properties. A total of 8 samples weighing 3 g each at different compositions (Zn4-xMxSb3) (M = Cu, Al) (x= 0, 0.3, 0.6 at.%) were prepared via powder metallurgy technique and followed by HIP sintering process. The relativedensity of all the samples recorded 85-95% which is comparable to the published data. From the XRD results, a near single phase of Zn4Sb3 was obtained. The SEM images revealed a minor of porous surface exist and showed metallurgical bonding formed in the prepared samples. From thermoelectric properties characterization, Cu showed as an effective element to lower the electrical resistivity as compared to Al when Sample 6 (Zn3.4Cu0.6Sb3) recorded 16.18×10-5 Ωm and Sample 8 (Zn3.4Al0.6Sb3) was 27.09×10-5 Ωm. The results showed that HIP sintering technique at lower temperature compare to other studies offers potential processing route to produce a good thermoelectric material associated with the doping element

Two-step synthesis of ca-based MgO hybrid adsorbent for pontential CO2 capturing application

Carbon capture and storage (CCS) is one of the method in reducing carbon dioxide (CO2) emissions into the atmosphere. CO2 capturing using calcium oxide (CaO) solid sorbents has been considered as an advanced concept for CO2 capture and recovery. However, the adsorption capacity of CaO decreases during repeated adsorption/desorption cycles. The stability of Ca-based sorbents during cyclic runs can be achieved via the incorporation of inert support materials. Among the available inert materials, MgO is most promising for CO2 due to high stability and a high Tammann temperature. Most of Ca- based MgO hybrid adsorbent synthesis methods sorbent come with its own limitations which are longer synthesis duration and complex or multistep methods. In this research, Ca-based MgO hybrid adsorbent was prepared via two-step method. Calcium acetate and magnesium nitrate as precursor had dissolved in water, follow by addition of ethanol. The mixture then became gelated and proceeded for calcination at 550oC and 650°C. The prepared sorbent was characterized by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and fourier transfer infrared spectroscopy (FTIR). The XRD analysis of the Ca-based MgO hybrid adsorbent showed the existence of MgO,CaO and CaCO3. FTIR analysis showed existant of CaO bond and MgO bond. The morphology of the hybrid adsorbent was found to be spherical to granular shape and agglomerated. The Ca- based MgO hybrid adsorbent structural and morphological shows great potential for CO2 capturing capacity over multiple carbonation cycles for CO2 capturing application

Assessment of corrosion on buried metallic pipeline induced by AC interference below high transmission line

High voltage alternating current (HVAC) transmission line is usually shared the same right of way with buried metallic pipeline. Long-term exposure of inductive coupling on buried metallic pipeline will cause AC corrosion at any coating defects on the pipeline. In the West Coast of Malay Peninsula, the AC-induced corrosion is not well studied, and the preventive maintenance is not taken into consideration by some of the pipeline operators. The objective of this paper is to assess AC corrosion susceptibility of the buried metallic multiproduct pipeline (MPP), which is cross or parallel to the HVAC along West Coast of Malay Peninsula. This MPP is laid from Sg. Udang, Melaka to distribution terminal in Dengkil, Selangor with approximate distance of 130 km. It was identified that along the pipeline routing, only 16 locations of MPP sections are cross and parallel to the HVAC. Standard industrial practice and equipment were used to conduct this corrosion assessment. Cathodic protection (CP) potential and AC output are measured using multimeter, clampmeter and Cu/CuSO4 reference electrode. While soil resistivity is determined by using soil resistivity meter with the native soil sample at site. Magnetic field magnitude is determined by using Biot-Savart Law formula. The current density is calculated for each MPP sections, and the pipeline sections that are in the risk of AC corrosion are determined. On the other hand, the CP system affected by stray current are further analyzed. Three locations indexed as (TP 43, TP 102 and TP105) are found under risk of AC corrosion, which is in the range of 20–100 A/m2. As per standard industry practice such as NACE SP-0169 and PTS 30.10.73.10, AC corrosion is unpredictable for AC current density in between above-stated range. These three locations have the highest AC voltage output, the lowest soil resistivity value and the CP potential measured are under protected value. However, the effect of magnitude of magnetic field has no compelling correlation on the AC corrosion activity. In conclusion, AC voltage, soil resistivity and CP potential at the crossing and parallel section to the HVAC play a significant role to the behavior and severity of the AC corrosion on the metallic buried pipeline

Assessment of corrosion on buried metallic pipeline induced by AC interference below high transmission line

High voltage alternating current (HVAC) transmission line is usually shared the same right of way with buried metallic pipeline. Long-term exposure of inductive coupling on buried metallic pipeline will cause AC corrosion at any coating defects on the pipeline. In the West Coast of Malay Peninsula, the AC-induced corrosion is not well studied, and the preventive maintenance is not taken into consideration by some of the pipeline operators. The objective of this paper is to assess AC corrosion susceptibility of the buried metallic multiproduct pipeline (MPP), which is cross or parallel to the HVAC along West Coast of Malay Peninsula. This MPP is laid from Sg. Udang, Melaka to distribution terminal in Dengkil, Selangor with approximate distance of 130 km. It was identified that along the pipeline routing, only 16 locations of MPP sections are cross and parallel to the HVAC. Standard industrial practice and equipment were used to conduct this corrosion assessment. Cathodic protection (CP) potential and AC output are measured using multimeter, clampmeter and Cu/CuSO4 reference electrode. While soil resistivity is determined by using soil resistivity meter with the native soil sample at site. Magnetic field magnitude is determined by using Biot-Savart Law formula. The current density is calculated for each MPP sections, and the pipeline sections that are in the risk of AC corrosion are determined. On the other hand, the CP system affected by stray current are further analyzed. Three locations indexed as (TP 43, TP 102 and TP105) are found under risk of AC corrosion, which is in the range of 20–100 A/m2. As per standard industry practice such as NACE SP-0169 and PTS 30.10.73.10, AC corrosion is unpredictable for AC current density in between above-stated range. These three locations have the highest AC voltage output, the lowest soil resistivity value and the CP potential measured are under protected value. However, the effect of magnitude of magnetic field has no compelling correlation on the AC corrosion activity. In conclusion, AC voltage, soil resistivity and CP potential at the crossing and parallel section to the HVAC play a significant role to the behavior and severity of the AC corrosion on the metallic buried pipeline

Microstructure and mechanical properties of porous aluminium composites reinforced with diamond particles

n the present work, diamond particles with various contents (5, 10 and 15 wt. %) were reinforced in porous aluminum (Al) composite via powder metallurgy technique. The desirable porous structure was designed by incorporating polymethylmethacrylate (PMMA) as a space holder material at fixed content of 30 wt. % in all the composites. Morphology of the resultant porous Al composite demonstrated the formation of uniform closed-cell macropores and diamond particles that are well bonded within the Al matrix. However, higher weight percentage (wt.%) of diamond content resulted in appearances of agglomeration and improper pore. X-ray diffraction (XRD) analysis confirmed strengthening intermetallic phases at the interfaces, thus improving the bonding strength and wetting action. The composites with 5wt.% and 10wt.% diamond content exhibited better compressive properties

Prediction and optimization on tribological behaviour of kenaf/carbon fiber reinforced epoxy matrix hybrid composites

The awareness on sustainability of the environment among the researchers leads to the exploration of natural fiber composite materials. Hybridization of synthetic fiber and natural fiber is one of the potential strategies to enhance the mechanical properties as well as the degradability of such composite materials. However, less information concerning the optimization of tribological properties of this hybrid composite is available in literature. The aim of this study is to propose a statistical model to predict and optimize wear and coefficient of friction of kenaf/carbon reinforced epoxy composite. The value of parameters; load and sliding velocity ranges from 10 to 30 N and 20.9 to 52.3 m/s, respectively, are used to assess wear and coefficient of friction (COF) of different stacking sequences using the Analysis of Variance (ANOVA). The tribological test was conducted using a pin-on-disc tribometer. Multifactorial design analysis was employed to optimize the test control variables. It was found that, the optimized factors that affects the coefficient of friction and wear is at load 30 N and sliding velocity of 52.36 m/s. The proposed statistical models for wear and COF have 99.5% and 97.6% reliability, respectively. The generated equation models are bounded within the wear test control factors and ranges. The outcome from this study will be very useful for main parameter prediction for an optimized wear and CO

Improvement in effectiveness of diamond in strengthening the porous aluminium composite

In this study, an aluminum (Al) alloy matrix reinforced with uncoated and titanium (Ti) -coated diamond were developed using powder metallurgy technique where polymethylmethacrylate (PMMA) particles were employed as space holders. The weight % of uncoated and coated diamond varied as (0, 6, 9, 12, 15, and 20 wt.%). Microstructural and elemental analysis was examined using scanning electron microscopy and energy dispersive spectroscope, respectively. The relative density and porosity that were in the range of 0.72–0.92 and 31–44% respectively, were measured using Archimedes principle. The compressive properties were measured and correlated with microstructure observations. The microstructure of the composite samples revealed presence of well-defined macro pores with good interfacial integrity. The X-ray diffraction revealed the presence of strengthening phases such as Al2Ti, Mg2Sn, AlB12, Cu5Sn6, Al12Mg17 and MgB2 phases formed as a result of addition of metal additives in Al matrix. Further improvement in the strength was obtained by using Ti-coated diamond particles as reinforcement. As Ti formed a good interface between the Al alloy matrix and the diamond thereby preventing the formation of undesirable carbide phases. There was an improvement in plateau stress and energy absorption capacity of 82 and 88% as compared to unreinforced porous sample. The maximum values obtained for the plateau stress and energy absorption capacity were 45.12 MPa and 13.68 MJ/m3 respectively for 9 wt.% of Ti-coated diamond reinforced composites. Uncoated diamond reinforced composites, on the other hand, reduced the strength of porous Al alloy matrix due to the formation of brittle intermetallic compound such as carbides (Al2C3) at the interface. As a result, the coated diamond particle surface modifies and improves the wettability of the Al alloy matrix and diamond interface

Effect of pore forming agent on phase transformation behavior of porous NiTi shape memory alloy

Porous NiTi shape memory alloy is of special interest for bioimplant materials due to its attractive features of NiTi dense structure such as low stiffness, high strength and excellent shape memory and pseudoelastic behavior. This porous NiTi can be produced via powder metallurgy technique using pore forming agent. The pore forming agent is used to create temporary pores that are occupied during sintering where the final sintered sample depends on the composition ratio of the pore forming agent. Porosity of up to 30–50% is predicted to be achieved which is similar to cancellous bone. However, there are queries whether the porous NiTi alloy produced may hinder the phase transformation behavior which is an indicator for shape memory behavior. Therefore, in this research, the effect of composition of pore forming agent such as calcium hydride, CaH2, on porosity level and how it correlates with phase transformation behavior of porous NiTi alloy were investigated. It shows that by increasing the percentage of CaH2 to 15 wt%, the porosity level of sintered sample can reach up to 42%. For phase transformation, there are martensitic transformation peaks observed for samples at a composition of ≤ 3wt% of CaH2 with enthalpy value of ~ 4.9 J/g. Increasing the percentage of CaH2 to ≥ 6wt%, the transformation enthalpy (ΔH) values drop significantly as the samples exhibit no martensitic transformation. This associated with the pores structure and undesirable phase that co-exist with NiTi formation, thus hindered the transformation enthalpy for porous NiTi