Ridvan Yamanoglu

Characterisation of nickel alloy powders processed by spark plasma sintering

Abstract In this study, nickel alloy powders were consolidated by spark plasma sintering. Experiments were performed between 700 and 750°C temperature range under 50 MPa pressure with holding times from 5 to 10 min. In addition to these main spark plasma sintering parameters three different heating rates ranging from 100 to 235°C min−1 and two different particle size ranges (75–106 μm narrow size distribution and −45 μm wide size distribution) were used for the experiments. After sintering, the sliding wear behaviour of the samples was investigated. The results revealed that the density of the material increased with raising the sintering temperature and holding time. However, heating rate and particle size also played an important role in the densification and these parameters were investigated in detail.

Effect of heat treatment on erosive wear behaviour of Ti6Al4V alloy

Abstract In this paper, the erosive wear behaviour of Ti6Al4V alloy depending on various heat treatment conditions was evaluated. It is aimed to understand the relationship between the microstructure and the erosion rate of Ti6Al4V alloys. Furthermore, the hardness and the surface morphology variations depending on the annealing parameters and the effects of these parameters on the erosion behaviour of the annealed Ti6Al4V alloy were also considered. Moreover, eroded surfaces of samples were examined by using a scanning electron microscope in order to understand dominant material removal mechanisms depending on the annealing parameters. Results showed that the aging process has dramatically affected the erosion resistance of Ti6Al4V alloy. The microstructure and the hardness of the samples have significantly affected the erosion resistance of the alloy. Surprisingly, erosion resistance decreased when the hardness increased. Finally, SEM investigations of the eroded surfaces of the heat treated samples showed that microcutting and microploughing were the dominant erosion mechanisms occurred during the erosion process.

Microstructural investigation of as cast and PREP atomised Ti–6Al–4V alloy

Abstract A microstructure characterisation of Ti–6Al–4V is conducted for cast, extruded and micrometre sized particles. The plasma rotating electrode process is used to produce spherical Ti–6Al–4V powders from an alloy electrode. The process parameters and their impact on the material properties are described. The effects of electrode rotation speed on the particle size distribution, particle shape and crystal structure are investigated in detail. Optical microscopy and scanning electron microscopy are used for microstructural characterisation. The analysis shows that cast and extruded Ti–6Al–4V alloys have equiaxial α and α+β phase structures, while plasma rotating electrode processed powder from the same alloy compositions has an acicular or martensitic (α) structure. The microstructure scale depends on the particle size. Microhardness measurements are used to assess mechanical property dependence on the microstructure of this alloy. The rapidly cooled alloy particles have much higher hardness than cast or extruded bulk alloy.

Sintering and microstructure characteristics of 42CrMo4 steel processed by spark plasma sintering

Rapidly solidified micron sized 42CrMo4 steel powder with a size range of 150–250 μm produced by plasma rotating electrode process was consolidated using a recently developed spark plasma sintering (SPS) process. The relationship between sintering parameters (temperature and soaking time) and microstructural properties was investigated. The effect of slow and high heating regimes on the consolidation of sintered compacts has been also investigated. Maximum relative density (99.2%) was obtained at 1000 °C, under 50 MPa pressure, with 8 min holding time and 200 °C/min heating rate. The microstructure of sintered steel was influenced by carburization occuring inside the graphite SPS process die. The diffusion of carbon produced martensite structure near the surface region and hardened the surface. This effect was investigated in detail using optical microscopy and hardness measurement. Scanning electrone microscopy was also used to examine the fracture surface of sintered compacts. High heating rate promoted the relative density at low temperature compared to high temperature.

Effect of nickel on microstructure and wear behaviour of pure aluminium against steel and alumina counterfaces

Abstract In this study, aluminium–nickel alloys with different Ni ratios ranging from 1 to 5 wt-% were produced by casting method. The effect of nickel on the microstructure and hardness properties was studied. The dry sliding wear response of the Al–xNi alloys against steel and alumina counterfaces was investigated. Worn surfaces of the alloys were examined using scanning electron microscopy. The results showed that the hardness of the alloys increases with increasing nickel content. Severe wear damage was observed at low and high nickel contents. Maximum wear resistance was obtained with the addition of 3 wt-% nickel to the pure aluminium under both loads and against both counterfaces.

Comparative evaluation of densification and grain size of ZnO powder compacts during microwave and pressureless spark plasma sintering

Abstract In this paper, ZnO powder was consolidated by microwave and pressureless spark plasma sintering (PL-SPS) processes. Comparative experiments are undertaken maintaining conditions of green density, temperature profile and applied pressure. Densification and microstructural characteristics are determined under similar sintering parameters, where the final relative densities of ZnO compacts were improved with increasing sintering temperature for both processing methods. Detailed microstructure investigation indicated that finer grain sizes with higher densification degree can be achieved by microwave sintering as compared with PL-SPS.

Mechanical properties of hypoeutectic Al-Ni alloys with Al3Ni intermetallics

Abstract In this paper, the effect of nickel content on the mechanical properties of aluminum were investigated. High purity Al and Ni were melted in an induction furnace and cast into a metal mold. Microstructural characteristic and mechanical properties of the alloys were studied in detail. The addition of nickel to pure aluminum increased the tensile strength and decreased the elongation at break value of the specimens. Maximum wear resistance was obtained with the addition of 3 wt.-% Ni. Further addition of nickel caused a decrease in wear resistance.

In Situ Aluminum Alloy Coating on Magnesium by Hot Pressing

Abstract In the present study, pure magnesium was in situ coated with pre-alloyed Al–Cu–Mg alloy through hot pressing. The produced samples were characterized by means of hardness, wear properties and microstructure characterization. A ball-on-disk test was used to determine the dry sliding wear characteristics of the compacts. The results showed that the hot pressing technique has been successfully applied for producing magnesium parts with compatible wear resistance and hardness to aluminum. The in situ coating of Al on Mg by hot pressing resulted in an increase in hardness of about 30% compared with the pure Mg substrate. The wear rate and friction coefficient of the samples decreased with Al coating and increased with an increase in the applied load during the wear tests, compared with the uncoated material.

MechanIcal and wear propertIes of pre-alloyed MolybdenuM p/M steels wIth nIckel addItIon

The aim of this study is to understand the effect of nickel addition on mechanical and wear properties of molybdenum and copper alloyed P/M steel. Specimens with three different nickel contents were pressed under 400 MPa and sintered at 1120oC for 30 minutes then rapidly cooled. Microstructures and mechanical properties (bending strength, hardness and wear properties) of the sintered specimens were investigated in detail. Metallographical investigations showed that the microstructures of consolidated specimens consist of tempered martensite, bainite, retained austenite and pores. It is also reported that the amount of pores varies depending on the nickel concentration of the alloys. Hardness of the alloys increases with increasing nickel content. Specimens containing 2% nickel showed minimum pore quantity and maximum wear resistance. The wear mechanism changed from abrasive wear at low nickel content to adhesive wear at higher nickel content.

Effect of Nickel Addition and Porosity on Fracture Behaviour of Molybdenum Alloyed Powder Metallurgical Steel

Abstract In the study for this contribution, good mechanical properties have been obtained from Mo (and Cu) alloyed PM-steels after suitable heat treatment. The influence of two to four weight percent nickel additions in these Mo (and Cu) alloyed PM-steels on the mechanical properties have been studied. The influence of such an alloying modification on the defect characteristics has also been investigated. The heat treatment of the steel material has been realized via a novel way, i.e. with the sinter-hardening method. The mechanical properties like tensile strength, matrix microhardness, and toughness have been measured. Transverse rupture tests have been implemented for toughness measurement while the transverse rupture strength data has been obtained by using the Weibull statistics. Microstructural studies have been performed with various microscopy techniques, where the general steel matrix was observed to exist of tempered martensite, bainite, residual austenite, and micropores. The amount of pores was measured with image analysis technique, while the amount of retained austenite was measured with the magnetic saturation method. The results show that the values of the transverse rupture test are determined primarily by pores/pore agglomerates that fit big size defect criteria. On the other hand, a positive effect of increasing Nickel content has been observed on the resistance against fracture.