Effect of copper addition on grain refinement of austenite in Fe-8wt.%Ni-(0.3)Wt.% Cu alloy

The effect of copper addition on martensitic structure and reversion from martensite to austenite behaviours upon heating were investigated to clarify mechanism of grain refinement of austenite in Fe-8wt.%Ni-Cu alloys. Upon water-quenching, the alloys underwent a martensitic transformation that exhibited a typical lath-martensitic structure. It was found that prior-austenite grain and martensite-packet sizes were refined with increasing copper content. The grain refinement was not due to a decrease of grain growth rate of the austenite. However, it was found that nucleation rate of the austenite on reversion was increased by the copper addition. In Fe-8wt.%Ni alloy heated in (austenite+ferrite) region, reversed austenite grains were formed at high angle boundaries such as prior austenite grain boundary and packet boundary. On the other hand, TEM observation of the Fe-8wt.%Ni-3wt.%Cu alloy revealed that fine copper particles precipitated within the martensitic structure and the reversed austenite grains also formed within lath-structures and lath boundary. It means that the copper addition promoted formation of the reversed austenite within martensitic matrix and resulted in the grain refinement of the prior-austenite in Fe-8wt.%Ni-Cu alloy

Influence of iron on phase stability and corrosion resistance of Ti-15%Cr alloy

In this study, the effect of Fe addition on the phase stability and corrosion resistance of Ti-15%Cr alloys was investigated. The alloying phenomenon in the specimens was also investigated to determine the effectiveness of the application of pure metallic powders as raw materials for the powder metallurgy method. Ti-15%Cr-1%Fe alloys exhibited needle-like structures within equiaxed structures, while Ti-15%Cr-5%Fe and Ti-15%Cr-10%Fe alloys only showed equiaxed grains. XRD results showed that the β phase could be stabilized by the addition of 5% or more Fe to the alloy. Although the pure powders were used as raw materials, the designated chemical composition, i.e. Ti-15%Cr-(1~10)%Fe can be achieved during sintering. The alloying phenomenon occurred upon sintering due to the high diffusivity of Cr and Fe within the β Ti matrix. The corrosion resistance of the newly developed Ti-15%Cr alloys was significantly improved compared with a commercial Ti-6%Al-4%V alloy

Plane Strain Fracture Toughness Determination for Magnesium Alloy

A stress intensity factor K was used as a fracture parameter to determine the true material property, i.e. plane strain fracture toughness KIC of AZ61 magnesium alloy using a single edge notch bend (SENB) specimen in accordance to ASTM E399 testing method. Five different specimen thicknesses of 2 to 10 mm were used in the test. A sharp fatigue pre-crack was initiated and propagated to half of specimen width at a constant crack propagation rate of about 1 x 10-8 m/cycle before the specimen was loaded in tension until the fracture stress is reached and then rapid fracture occurred. The fracture toughness KC values obtained for different thicknesses showed that KC value decreased with increasing specimen thickness. The highest KC value obtained was 16.5 MPa√m for 2 mm thickness specimen. Thevalue of KC became relatively constant at about 13 MPa√m when the specimen thickness exceeds 8 mm. This value was then considered as the plane strain fracture toughness KIC of AZ61 magnesium alloy. Calculation of the minimum thickness requirement for plane strain condition and the size of the shear lips of the fracture surface validate the obtained KIC value

Effects of heat input on metallurgical behavior in HAZ of multi-pass and multi-layer welded IN-939 superalloy

The hot components of a gas turbine are susceptible to damage in the high-temperature environment of turbine engine operation. Given that these components are relatively costly to manufacture, they are often repaired than replaced when damaged. Fusion welding is an economical method for repairing the damaged components of a gas turbine. This research examines the roles of heat input, pass number and layer number on the intergranular liquation cracking of the Inconel-939 (IN-939) precipitate nickel base superalloy during tungsten arc welding. Several specimens were welded with IN-625 filler alloy under argon gas by following the Taguchi method and an L8 array. These specimens were then characterized via metallographic investigations and hardness measurements. Results show that, during welding, the IN-939 heat-affected zone (HAZ) is acutely prone to cracks that propagate along the grain boundaries. Moreover, layer number, heat input and pass number significantly influence the microstructure and liquation cracking of HAZs with impact percentages of 72.37%, 22.17% and 4.84%, respectively

STRESS RELAXATION BEHAVIOUR AND MECHANISM OF HEAT TREATED INCONEL 718 IN HIGH TEMPERATURE ENVIRONMENTS

The stress relaxation behaviour of heat treated nickel-base superalloy Inconel 718 at high temperature was investigated. Solution treatment was applied on the as-received material at 980 oC for 1 hour before water quenching followed by double aging treatments at 720 oC for 8 hours and 621 oC for 8 hours, then cooled in air. The stress relaxation test was conducted at 1 % strain at different test temperatures of 550 oC, 650 oC and 750 oC. The tests were carried out for a total of 72 hours. The tests were interrupted at 3 hours and 48 hours to investigate the evolution of microstructure and changes in material properties by using Scanning Electron Microscope (SEM) and X-Ray Diffractometer (XRD). The results showed that thermal dependent stress increased with decreasing temperature. In contrast, stress relaxation rate increased with increasing temperature. Microstructure observation by SEM showed that recovery process occurred. This was further supported by the decrease in dislocation density with increase in time and temperature, which is in-line with the Vickers micro-hardness results

Pembentukan mikrostruktur berbentuk sfera dalam keadaan separa pepejal aloi aluminium Al-4.8Si-2.8Cu-0.5Mg

Hasil penyelidikan mengenai pembentukan mikrostruktur berbentuk sfera dalam keadaan separa pepejal aloi aluminium Al-4.8Si-2.8Cu-0.5Mg dibentangkan dalam penulisan ini. Bahan awal aloi aluminium tersebut dihasilkan melalui proses tuangan konvensional. Mikrostruktur bahan awal terdiri daripada struktur dendrit dan antara dendrit yang halus. Mikrostruktur aloi berubah kepada bentuk bukan dendrit (bentuk roset) yang halus apabila leburan bahan awal aloi tersebut dituang ke atas plat keluli cerun penyejuk yang dicondongkan pada sudut kecondongan 60° dengan suhu tuangan 650°C dan panjang cerun penyejukan 400 mm, sebelum dibiarkan memejal di dalam acuan keluli yang dipanaskan terlebih dahulu pada suhu 150°C. Pembentukan mikrostruktur berbentuk sfera dalam matriks cecair berjaya dihasilkan apabila bilet aloi yang mengandungi mikrostruktur bukan dendrit dipanaskan semula secara pantas sehingga suhu separa pepejalnya pada 575°C dengan menggunakan sistem pemanasan secara aruhan berfrekuensi tinggi (30-80 kHz, 35 kW). Bilet aloi yang berada dalam keadaan separa pepejal berjaya dibentuk-tikso ke dalam acuan keluli yang dipanaskan terlebih dahulu dengan menggunakan mesin penekan silinder hidraulik yang membekalkan daya tekanan 20 kN dengan kelajuan maksimum 85 mm/s. Hasil daripada proses pembentukan-tikso menunjukkan ira matriks α-aluminium yang berbentuk sfera bertaburan secara seragam di samping tidak terdapat keporosan di sepanjang sampel. Proses rawatan haba T6 yang melibatkan rawatan haba larutan pada 480°C selama 8 jam, lindapkejut dalam air panas pada suhu lebih kurang 60°C dan diikuti proses penuaan pada suhu 155°C selama 4 jam dilihat menyumbang kepada taburan partikel-partikel dengan lebih sekata

Two component injection moulding of bi-material of stainless steel and yttria stabilized zirconia – green part

The two component injection molding (2C-PIM) is a promising technique for production of small, complex and high density, metal-ceramic parts in large scales. This method is a viable option for integrating incompatible functions or properties of the materials in a singular part or component. Thus, the production of near net shaped components via 2C-PIM is imperative due to cost effectiveness resulting from high unit volumes. In this study, the feasibility of joining stainless steel (17-4PH) and 3mol% yttria stabilized zirconia (3YSZ) materials in their green states was investigated. Two feedstock of SS17-4PH and 3YSZ powder materials was prepared based on optimum solid loading of 3vol% lower than value of the critical loading. The critical solid loading for the SS17-4PH and 3YSZ powder materials were 71vol% and 53vol% respectively, based on the oil absorption technique ASTM: D-281-12. The binder system utilized comprises of 60wt.% palm stearin (PS) and 40wt.% low density polyethylene (LDPE). The two materials were injected sequentially using the screw type injection molding machine (BOY 22A) to form a bi-material component. The green properties were investigated. The morphology of the individual green parts and composites depicted that the powders were optimally dispersed in the binder matrix indicating good mixture and compaction of the green components. The flexural strength of the single components of the bi-material was above 5 MPa. The strength of the bonding zone which was 1.4 MPa indicates an evidence of bonding

The Characterization and Rheological Investigation of Materials for Powder Injection Moulding / Ukwueze Bonaventure Emeka...[et al.]

Stainless steel and Zirconia have become an attractive choice of powder injection moulding (PIM) materials because of their respective excellent mechanical and thermal properties. These are often combined deliberately to produce functional graded components. The characterization and rheological investigations of the materials are thus indispensable for successful implementation of subsequent stages to the PIM process. In this investigation, the powder materials were characterized. Two feedstock with solid loadings of 68% for stainless steel (17-4PH) and 50% for 3mol% yttria stabilized zirconia (3YSZ), were prepared based on optimal loading of 3% lower than the critical value. A common binder was employed comprising of 60% palm stearin and 40% polyethylene. The rheological results for the two materials exhibited pseudo-plastic and shear thinning behaviour indicated by decrease in velocity with increasing shear rate. The results also show that a temperature of 1300C is considered appropriate for injection moulding of both feedstock

Ballistic Limit of Laminated Panels with Different Joining Materials Subjected to Steel-Hardened Core Projectile

This paper presents the computational-based ballistic limit of laminated metal panels comprised of high-strength steel and aluminium alloy Al7075-T6 plates to necessitate a weight reduction of 25% in the existing armour steel plate using three different joining materials. Numerical models of the triple-layered panels were developed using the commercial Explicit Finite Element code and were impacted by a 7.62-mm armour-piercing projectile at velocities ranging from 400 m/s to 1000 m/s. The ballistic performance of each configuration plate in terms of the ballistic limit velocity, depth of penetration and end of penetration, was quantified and considered. It was found that the panels with joining materials exhibited a better ballistic limit on an average of 1.5% than that of the panel without a joining material. The penetration depth of the panel joined by polyurethane possessed the lowest depth of 22 mm with a higher contact duration compared to the panel without a joining material. This happened because the polyurethane adhesive was better able to absorb energy at a high strain rate impact than the other joining materials. Thus, based on the investigation that was carried out, polyurethane seems to be the most interesting option for joining different metals of Ar500 and Al7075-T6 as a laminated panel for armoured vehicle applications

Determining the effects of aging on halloysite nano-tube modified binders through the pull-off test method

Aging changes the chemistry of bitumen and this adversely affects bitumen’s adhesion with aggregate. For this reason, the use of pull-off test was proposed to evaluate bitumen’s adhesion during different aging stages. In this study, the pull-off test method is used to evaluate the effects of aging on a 60/70 penetration grade bitumen and binders modified with 2 and 4% halloysite nano-tube (HNT). The short-term aging (STA) and long-term aging (LTA) of unmodified and modified bitumens were simulated using the rolling thin film oven (RTFO) and pressure aging vessel (PAV) tests respectively. The pull-off test was conducted using the universal testing machine (UTM). Stainless steel and granite substrates moulds were designed and fabricated for this purpose. Dry and wet conditions were simulated to evaluate the loss of bonding strength due to aging. Additionally, consistency tests, namely penetration test, softening point test, and viscosity test, were conducted on all binders. The activation energy (AE) for unaged and aged binders were also evaluated. The results for the consistency test; the pull-off test for stainless steel substrate; and the values for AE showed that the addition of the HNT decreased the effect of aging, which means that modified binders showed decreased temperature susceptibility and this is reflected in improved aging resistance. The result of the pull-off test on granite substrate showed that binders modified with HNT performed better under dry and wet conditions. It can be concluded that HNT is an anti-aging as well as anti-striping agent