Increase In Number Of Passes Research Articles

Tribological studies on aluminum beryl composites subjected to ECAP process

The strengthening processes of aluminum alloys and their composites are generally assessed after precipitation hardening or following different laid down strain hardening procedures such as Equal Channel Angular Pressing (ECAP), Multi-Axial Forging (MAF), High-Pressure Torsion (HPT), Accumulative Roll Bonding (ARB), etc. Among them, ECAP is considered to be a novel method of producing fine-grained structure with different properties. On-going through the available literature, it is noted that the adoption of ECAP in Aluminum metal matrix composites, especially the Aluminum Beryl composites and then assessing their tribological responses, are scarce to come across. Hence, this particular aspect is addressed in this work.In the present investigation, Al 2024 alloys containing 6% Beryl particles, produced by stir cast route and subjected to ECAP operation up to two passes, have been assessed for slide wear and coefficient of friction (CoF) properties for comparison with un-reinforced Al 2024 alloy for qualitative and quantitative evaluation purposes. The wear and friction evaluation are carried out using the well-known Pin-On-Disc (POD) apparatus for three different loads (49 N, 91 N, and 136 N) and sliding distances (2000, 4000 and 6000 m) at a constant sliding speed of 1.67 m/s.The data reveals that the wear loss decreases with increase in the number of passes due to increase in hardness & decrease in grain size for all the three loads and sliding distances employed. Further, the wear losses show an increasing trend with an increase in the applied load. Also, it is observed that the CoF decreases with increase in number of passes at all loads. It is high in the as cast state and it increases with increase in load. It is inferred from the present findings that the ECAP has made a significant impact on the wear behaviour of Al-Beryl composites, thus emphasizing the fact that the composites are suited for wear resistance applications such as in production engineering sectors.

Eptifibatide use in ischemic stroke patients undergoing endovascular thrombectomy: A matched cohort analysis.

IntroductionSmall studies have suggested that eptifibatide (EPT) may be safe in acute ischemic stroke (AIS) following intravenous thrombolysis or during endovascular therapy (EVT) for large vessel occlusion (LVO). However, studies are called upon to better delineate the safety of EPT use during EVT.MethodsA comprehensive stroke center registry (09/2015-12/2020) of consecutive adults who had undergone EVT for anterior LVO was queried. Patients treated with EPT were matched with 2 control groups based on known factors associated with intracranial hemorrhage (ICH) risk - age, Alberta Stroke Program Early Computed Tomography Score (ASPECTS), and number of thrombectomy passes. Safety outcomes (intracranial hemorrhage [ICH], parenchymal hematoma [PH-2] grade hemorrhagic transformation, symptomatic ICH [sICH]) and efficacy outcomes (TICI 2B/3 recanalization, 24-h National Institutes of Health Stroke Scale [NIHSS] score), were compared between matched groups using descriptive statistics. In addition, multivariable logistic regression was used to assess for an association between EPT and PH-1/PH-2 grade hemorrhages.ResultsA total of 162 patients were included, 54 of whom (33%) received EPT. The rate of ICH was similar between groups (p = 0.62), while PH-2 was significantly more frequent with EPT (16.7% EPT vs. 3.7 vs. 1.9%; p = 0.009), but without significant differences in sICH (5.6% EPT vs. 7.4 vs. 3.7%; p = 0.72). Rates of TICI Score ≥ 2B were nominally higher with EPT use (83.3 vs. 77.8 vs. 77.8%, p = 0.70). Between the EPT and control groups, there were no differences in 24-h NIHSS (p = 0.09) or 90-day mortality (p = 0.58). Our adjusted multivariate analysis identified that the number of passes (p < 0.01), EPT use (p < 0.01), and tandem occlusion (p = 0.03) were independent predictors of PH1/PH2 grade hemorrhage. Additionally, every unit increase in number of passes resulted in a 1.5 times greater odds of a high-grade hemorrhagic transformation in EPT-treated patients (adjusted OR = 1.594).ConclusionIn this single-center analysis, EPT use during EVT was associated with a significantly higher rate of PH1/PH2 grade hemorrhages, but not with differences in sICH, 24-h NIHSS, or 90-day mortality. Randomized prospective trials are needed to determine the safety and efficacy of EPT in this population.

Characterization of the topography generated by low plasticity burnishing using advanced techniques

This work investigates the surface topography of AISI 304 austenitic stainless steel after low plasticity burnishing through the evaluation of the average surface roughness (Ra), surface texture direction, areal power spectral density (APSD), scale-sensitive fractal analysis and continuous wavelet transform (CWT). The reason for adopting these approaches resides in the fact that traditional amplitude profile parameters neglect dynamic aspects of the process and geometric features of the burnished surface. The direction, periodicity and anisotropy of the surface texture were influenced by number of passes and burnishing speed and, in general, less severe plastic strain conditions tended to produce surfaces with strongly anisotropic characteristics, preferred direction of motifs, with power spectrum indicating a well-defined spatial frequency of peaks, lower fractal complexity and uniform profile distribution. The increase in surface strain severity produced surfaces with more diffuse directional characteristics, which tended to present surface isotropy, higher spatial frequency dispersion of the peaks and higher fractal complexity. Furthermore, the transition from an anisotropic to an isotropic surface can occur without changes in the average surface roughness. The continuous wavelet transforms analysis indicated a dynamic variation on the surface plastic strain when burnishing. The intermediary burnishing speed induced a strong disturbance with loss of periodicity of the roughness profile, resulting in a remarkable influence on the roughness profile in small scales. The increase in number of passes elevated the plastic strain severity, affecting the surface macrogeometric profile. The isotropic surface promoted a less severe stress concentration, reducing the tensile stresses and retarding crack nucleation, thus increasing the fatigue considerably.

Synthesis of radar-absorbing NiFe2O4 nanoparticles and effects of pass number on mechanical properties of AA7075/NiFe2O4 surface nanocomposites fabricated by FSP

In this paper, first, the desired NiFe2O4 nanoparticles were produced using the hydrothermal method then the AA7075/NiFe2O4 surface nanocomposite was fabricated by the friction stir processing (FSP) method. The results show that the hydrothermal method is very suitable for making NiFe2O4 nanoparticles with a fine and uniform structure that the fabricated nanoparticles have a superparamagnetic property that can be used for radar-absorbing coatings. The nanoparticles were well distributed in the base AA7075 aluminum alloy sheet in addition to the fine-grained structure achieved using FSP. The microhardness of the FSPed and surface nanocomposites were significantly improved compared to the base metal and increased with the increasing pass number of FSP. Also, the tensile properties consist of the ultimate tensile strength (UTS), formability, and toughness decrease with increasing the number of FSP passes.

The effect of material position of multi-pass friction stir processing on friction stir welded AA1050/AA6082 dissimilar joints

The AA1050 and AA6082 plates were used in producing dissimilar joint through friction stir welding (FSW) technique. The developed dissimilar joint was then subjected to multi-pass friction stir processing (FSP) technique. Various tests for the AA1050/AA6082 (AA1050 on the advancing side) and AA6082/AA1050 (AA6082 on the advancing side) joints were conducted on joints subjected to 1pass (1P) and 4pass (4P). The microstructural analysis showed that the increase in number of FSP passes resulted in a reduced grain size regardless of the of material position. The Vickers microhardness for AA1050/AA6082 FSPed joints increased towards AA6082 side while the microhardness for AA6082/AA1050 FSPed joints decreased towards the AA 1050 side regardless the number of the passes. The ultimate tensile strength (UTS) of AA1050/AA6082 joint increased with an increase in the number of passes while AA6082/AA1050 fluctuated between the specimens sampled from different locations of the FSPed joints.

Microstructural and mechanical characteristics of AA1050/mischmetal oxide in-situ hybrid surface nanocomposite by multi-pass friction stir processing

Surface hybrid in-situ aluminum matrix nanocomposite (AMNC) was fabricated by multi-pass friction stir processing (FSP) and a tool traversing speed of 100 mm/min and rotating speed of 1600 rpm with an objective to enhance mechanical properties. Mischmetal oxide (MMO) powder with an initial size of 50 nm, at a concentration of 8.5 vol% was used as the reinforcing particles. EDS particle analyses revealed in-situ solid-state chemical reactions between the Al matrix and the MMO particles. The reaction products, MM3Al and MM3Al11, were distributed uniformly in the discontinuously dynamic recrystallized nano and UFG microstructure. Increasing pass number improved the particle distribution and decreased agglomerated particle size while promoting the in-situ solid-state reaction. The nanocomposite produced by 6 FSP passes enhanced yield stress, 180% (YS = 70 MPa) and strength, 120% (UTS = 132 MPa) while reduced the tensile ductility from 35% to 23%. Fractographic studies showed that dimple-shape ductile fracture mode changed to ductile-brittle mode.

Aerosol Jet Printing of Ti3C2 Mxene Aqueous Ink

An emerging class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, known as MXenes have garnered significant interest in the scientific community due to their unique electrical, optical, and chemical properties [1]. Studies have reported high electrical conductivity and response, surface hydrophilicity, compositional control, and mechanical strength [1]. This unique combination of properties makes MXenes a contender for a wide variety of applications including batteries, super-capacitors, electronics, sensors, and others [2]. However, for MXenes to become industrially relevant, their compatibility with large scale synthesis and manufacturing techniques needs further investigation. In this study, we report the first aerosol jet printing (AJP) of water based titanium carbide (Ti3C2) MXene ink on a flexible polyimide substrate (Fig. 1-a,b). AJP is a high resolution additive manufacturing technique expected to shorten production times, provide greater control over size, design and variability, and a demonstrated capability of conformal printing and flexible substrate processing [3]. Previous studies have reported nano-material inks composed of various 2D materials including molybdenum disulfide, black phosphorous and hexagonal boron nitride [4]. However, only graphene-based inks have been shown to be AJP compatible [5]. Compared to graphene, MXenes offer greater compositional control. About 30 different kinds of MXenes have been synthesized, while many more are theoretically studied [1]. 2D Ti3C2 was the first to be discovered and has been studied most extensively [6]. To develop our AJP MXene ink, multi-layer MXenes were obtained by in situ HF etching of the pre-cursor Ti3AlC2 MAX Phase [7]. The obtained colloidal solution, containing 2D MXene flakes was sonicated with deionized water for 3 hours at 55 W. The resultant ink had a concentration of 1 mg mL-1 and an average flake size of 100 nm +/- 10 nm, as confirmed by dynamic light scattering (DLS) measurements. Contact angle measurements of the ink on polyimide substrate revealed an angle of 58.13o (Fig 1-c), showing good wettability. Our aqueous ink was printed with Optomec AJ-200 printer using the ultrasonic atomizer and printer parameters such as nozzle diameter, sheath gas flow, atomizer gas flow, atomizer current and platen temperature were optimized to get even dispersion and uniform printing. The MXene solutions were then printed in 0.5 mm x 1 cm linear structures with varying pass numbers (N), N = 5 to N = 25 in 5 pass increments. To investigate the quality of the printed structures, optical microscopy, height measurements, scanning electron microscopy (SEM) imaging and two-point probe resistance measurements were carried out. As revealed by optical images, the lines were even and didn’t show overspray, “coffee ring” effects, or runs typically associated with a solvent rich print (Fig. 1-d). SEM also showed even dispersion and consistent printing (Fig 1-e). However, some microcracks could be seen within the lines; which could be due to the absence of an annealing treatment. Stylus profilometer was used to determine the height of our printed MXene lines which varied from ~ 620 nm to 4.80 µm (Fig. 1-f). Our most uniform prints were N = 15 and N = 20 which had a height of 2.50 µm +/- 0.10 µm and 3.50 µm +/- 0.10 µm, respectively (Fig. 1-f). Electrical resistance (R) varied from R = 568 to R = 60 kΩ for N = 5 and N = 25 respectively (Fig. 1-g). In conclusion, we report the first AJP of aqueous Ti3C2 MXene inks. We find that the dimensions and electrical resistance of AJP MXene devices scale with increasing pass number, as expected. Microscopy analysis suggests additional work remains to be done to optimize our ink rheology and post-processing. However, our work highlights the important potential of additive manufacturing of MXene based devices which could include microelectrodes, battery electrodes, thermoelectrics, micro-capacitors and flexible sensors. [1] B. Anasori, M. R. Lukatskaya, and Y. Gogotsi, Nature Reviews Materials, 2 (2017). [2] K. Hantanasirisakul and Y. Gogotsi, Advanced Materials, 1804779 (2018). [3] A. A. Gupta, A. Bolduc, S. G. Cloutier, and R. Izquierdo, 2016 IEEE International Symposium on Circuits and Systems (ISCAS) (2016). [4] G. Hu et al., Chemical Society Reviews, 47, 3265–3300 (2018). [5] T. S. Tran, N. K. Dutta, and N. R. Choudhury, Advances in Colloid and Interface Science, 261, 41–61 (2018). [6] M. Naguib et al., ChemInform, 42 (2011). [7] M. Alhabeb et al., Chemistry of Materials, 29, 7633–7644 (2017). Figure 1

Grain refinement and mechanical properties of metals processed by constrained groove pressing

Constrained groove pressing (CGP), as a new severe plastic deformation technique, can be used for fabricat ing high performance sheet materials. Because of its potential for largescale industrial production, CGP is prospective for application in aviation, aerospace, transportation and many other fields. In this work, Cu-Zr and titanium (CP-Ti) sheets were processed by CGP. Microstructures of these two kinds of sheets before and after CGP were analyzed and the grain sizes were moderately refined after two-pass CGP processing. Mechanical testing results show that Vickers hardness, yield stress and ultimate strength of Cu-Zr alloy after two-pass CGP increased by 70%, 273% and 64% respectively, while those of CP-Ti increased by 26%, 66% and 48% respectively comparing with the unprocessed material. These two kinds of materials exhibit pronounced positive st rain rate sensitivity (SRS) and the SRS of Cu-Zr alloy increases with increasing pass number of CGP, while the SRS of CP-Ti is not so sensitive. The strengthening mechanism analysis indicates that the stress elevation after CGP is mainly due to dislocation accumulation and interaction, while grain boundary strengthening is not significant. The grain refinement efficiency of CGP is comparatively studied with respect to other SPD methods.

Estimation Of Fatigue Crack Propagation Rate Of Al 6061 Alloy Process By Multi-Axial Compression

Abstract Al 6061-T6 alloy was solution treated and then multi-axial Compression (MAC) was done with cumulative true strain of 0.6,1.2 and 1.8 in three, six and nine passes respectively. The dimension of the specimen was taken in the ratio of 1.22:1.13:1. The grain size of the specimen was also deceased with increasing the number of passes. The grain size measured after zero, three, six and nine pass of multi axial compression was 54 µm, 21 µm, 9 µm and 6 µm respectively. At constant ΔK the fatigue crack growth rate (da/dn) of the material decreases with increase in the number of passes in multi-axial compression. The reduction of the grain size might be one reason for increased fatigue life of the material. While crack deflection and crack branching were the other reason for increased fatigue life. The crack deflection and crack branching both increases with increase in number of passes.

Mechanical behaviour and thermal stability of multi-axially compressed copper

In the present study coarse grained (CG) annealed copper is subjected to multi-axial compression (MAC) process up to 9 passes to analyse its mechanical behaviour and thermal stability. The samples are characterized by optical microscopy to analyse microstructure evolution and grain size during MAC process. Mechanical properties like hardness and tensile strength have been evaluated by conducting the hardness and tensile test at ambient temperature. Microstructural examinations reveal the reduction in grain size with increase in number of passes which contributes to enhanced hardness and strength of copper. Tensile fractured specimens are examined under scanning electron microscope (SEM) to analyse the mode of failure with increasing number of MAC passes. Fractured micrographs reveal the ductile mode of failure in annealed and lower pass sample which is further converted to mixed mode (ductile and brittle) as the number of passes increased. Thermal stability of processed copper is also analysed by differential scanning calorimetry (DSC) analysis and results reveal reduction in thermal stability with increase in number of MAC passes. The evaluated properties of processed copper are correlated with microstructures.

Mechanical Properties of Friction Stir Processed Al6061-BN Surface Composite

This paper reports on mechanical behaviour of friction stir processed Aluminium 6061 - Boron Nitride surface composite. Percentage of Boron Nitride was varied from 0 to 6wt% in steps of 3wt%. Effect of Number of pass and reinforcement content on Microstructure (optical and SEM), hardness and tensile behaviour of Al6061 was evaluated. Results shows that composite exhibited higher hardness & tensile strength when compared to unreinforced ones. Increase in number of passes increases the hardness and tensile strength of both alloy & composite

Microstructure, Property Changes and Characterization for ST 35 Steel Material during Multiple Pass Cold Drawing Process of Seamless Tubes

Cold drawing is metal working process utilising tensile forces to deform the metal. This paper reports the microstructure and mechanical properties correlation with each stage of multi-pass cold drawing of ST 35 steel in the process of seamless tubes manufacturing. The microstructural evaluations showed that there is grain elongations as the number of passes increases. The same findings can be validated using Scan Electron Microscope (SEM). In addition, the mechanical testing values on UTM are examined with the number of passes. The results of this study shows that the mechanical properties, variation in grain size and hardness has correlation with the resulting microstructure of the material which are evaluated with the increase in number of passes. First pass before heat treatment shows better properties.

Effect of Pressing Speed on Al-Mg-Si Aluminium Alloy Processed by Repetitive Corrugation and Straightening

Repetitive Corrugation and Straightening (RCS), a promising Severe Plastic Deformation technique (SPD) is used to produce ultrafine grained (UFG) / nanostructured material in coarse grained structure. In this work, Al-Mg-Si aluminium alloy was subjected to RCS process at two different pressing speeds (0.5 and 2.0 mm. sec -1 ) with the RCS die having equal breadth and height of 5 mm and the groove angle (θ) of 30°. The specimens were processed to the maximum of 8 numbers of passes. The microstructural features were studied using TEM. TEM micrographs confirm the formation of dislocation cell in Al-Mg-Si alloy after 8 pass at room temperature processing condition. The sub-grain formation related to the strength. Tensile strength and hardness of the RCSed specimen were studied and compared in order to study the effect of pressing speed on the properties. The strength and hardness were high in the specimen prepared at low pressing speed. The hardness value increased to 86 HV and 96 HV at the end of 8 passes respectively for 1 mm. sec -1 and 0.5 mm. sec -1 respectively, originally form 69 HV. The strength increases in a linear manner with the increase in number of passes. The strength increased to 187 MPa at the end of 2 pass processed with the pressing speed of 0.5 mm. sec -1 and 178 MPa at the end of 6th pass processed with the pressing speed of 2 mm. sec -1 . The unprocessed alloy shows 70 MPa as strength.

Microstructure evolution and mechanical properties of nano-SiCp/AZ91 composite processed by extrusion and equal channel angular pressing (ECAP)

Nano-SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were extruded at 350°C, then processed by equal channel angular pressing (ECAP) at various temperatures (250°C, 300°C and 350°C). Grains are significantly refined after the extrusion and the ECAP. A basal fibre texture was detected by neutron diffraction after the extrusion, which inclines about 45° to the extrusion direction (ED) after the ECAP. Nano-scaled SiC particles agglomerate in the as-cast composite. After the extrusion, the agglomeration tends to form continuous or discontinuous strips along the extrusion direction. By application of the ECAP, the agglomerated SiC particles are partly dispersed and the strips formed during the extrusion tend to be thinner and broken with the increasing pass number. The yield tensile strength (YTS) and the ultimate tensile strength (UTS) of the composite are dramatically increased after the extrusion. ECAP for one pass at various temperatures further increases the strength, however, the YTS decreases with the increasing ECAP temperature and the pass number. The Orowan equations predict the maximum YTS of the composite may be up to 400MPa providing SiC particles are homogenously distributed in the matrix.

Friction stir processing of Al–CNT composites

Friction stir processing (FSP) is a solid-state process with the ability to refine grain sizes and uniformly disperse particles to improve the mechanical properties of the base material. In this study, FSP was performed on AA6061-T6 with and without additions of multi-walled CNTs. For FSP on monolithic Al plates, dendrites were broken down and dispersed uniformly with the increase in number of passes. As for FSP of Al–CNT composites, the CNTs have been successfully dispersed with three FSP passes. Dispersion is more uniform with increasing number of passes. The Vickers hardness and tensile yield strength were found to have improved after performing FSP with the addition of CNT as compared to FSP of AA6061-T6 without CNT.

Nanoscratching of Optical Glass Surfaces Near the Elastic–Plastic Load Boundary to Mimic the Mechanics of Polishing Particles

The nanomechanical deformations on glass surfaces near the elastic–plastic load boundary have been measured on various glasses by nanoscratching using an atomic force microscope (AFM) to mimic the mechanical interactions of polishing particles during optical polishing. Nanoscratches were created in air and aqueous environments using a 150‐nm radius diamond‐coated tip on polished fused silica, borosilicate, and phosphate glass surfaces; the topology of the nanoscratches were then characterized by AFM. Using load ranges expected on slurry particles during glass polishing (0.05–200 μN), plastic‐type scratches were observed with depths in the nm range. Nanoscratching in air generally showed deeper &amp; narrower scratches with more pileup compared to nanoscratching in water, especially on fused silica glass. The critical load needed to observe plastic deformation was determined to range from 0.2–1.2 μN for the three glasses. For phosphate glass, the load dependence of the removal depth was consistent with that expected from Hertzian mechanics. However, for fused silica and borosilicate glass in this load range, the deformation depth showed a weak dependence with load. Using a sub‐Tg annealing technique, material relaxation was observed on the nanoscratches, suggesting that a significant fraction of the deformation was due to densification on fused silica and borosilicate glass. Repeated nanoscratching at the same location was utilized for determining the effective incremental plastic removal depth. The incremental removal depth decreased with increase in number of passes, stabilizing after ~10 passes. In water, the removal depths were determined as 0.3–0.55 nm/pass for fused silica, 0.85 nm/pass for borosilicate glass, and 2.4 nm/pass for phosphate glass. The combined nanoscratching results were utilized to define the composite removal function (i.e., removal depth) for a single polishing particle as a function of load, spanning the chemical to the plastic removal regimes. This removal function serves as an important set of parameters in understanding material removal during polishing and the resulting workpiece surface roughness.

Numerical investigation of effects of deformation allocation on multi-pass conventional spinning process of curvilinear generatrix parts

Deformation allocation has significant effects on the process of multi-pass conventional spinning, especially for the curvilinear generatrix parts. Three different patterns of deformation allocation for curvilinear generatrix parts, including equal max deformation, equal arc length, and equal axial distance, are proposed and defined. Roller path profiles are designed based on them respectively. A 3D elastic-plastic finite element model is developed to investigate the effects of deformation allocation on forming quality and efficiency of the multi-pass spinning of curvilinear generatrix parts, based on the designed paths. The results show that a reasonable deformation allocation in each pass can improve the efficiency of the process effectively. The equal max deformation pattern can lead to better wall thickness distribution and forming efficiency. However, the fittability of it is poorer, compared with the others. This phenomenon is more significant with the increase of pass number.

Evaluation of Shearing Rolls for Hulling Confectionary Sunflower Seed for Precision Planting

<abstract> <bold><sc>Abstract. </sc></bold>The planting of sunflower seed has always used intact inshell seed. However, consumer demand for extra-large (XL) confection sunflower seed has led to new hybrid varieties, and much of the seed is now too large for current planting technologies and has poor germination. One alternative may be to use hulled kernels. Unfortunately, the impact hullers used in the snack food industry cause very high kernel breakage and poor germination. Thus, the effectiveness of shearing rolls was evaluated across several process conditions including: seed moisture content (6.1%, 7.8%, and 8.5%), differential roller speed (1.29, 1.55, and 1.68), roller gap distance (0.14 and 0.21 cm), and number of roller passes. Overall hulling effectiveness increased with decreased seed moisture content, and increased roller speed. At 6.1% moisture content, 0.21 cm roller gap distance, and 1.29 roller speed, proportion of dehulled seed increased by 54%, but the fraction of intact seed decreased by 19% when number of passes increased from 1 to 5. Although intact kernel yield improved with increasing pass number, germination and vigor index declined when the number of passes exceeded five, regardless of seed moisture and roller speed. The highest intact kernel yield of 68% with 88% germination and overall hulling efficiency of 4.9 was obtained using 7 passes, seed moisture content of 6.1%, and differential speed of 1.68. The results suggest shearing rolls provide a vast improvement of intact kernel yield and germination when compared to impact hulling used in the industry.

Wear properties of brass samples subjected to constrained groove pressing process

Ultrafine grained materials have experienced a rapid development during the last two decades. Constrained groove pressing (CGP) process is one of the severe plastic deformation methods to fabricate ultrafine grain sheet materials. In this research, wear behavior of brass sheet subjected to CGP process was investigated. Generally it is shown that CGP process enhances the wear resistance of the material and this behavior is improved by increasing pass number. Also, the effect of initial pass and lower applied normal load on the wear resistance is more profound than subsequent passes and higher applied normal load, respectively. In addition, the influence of normal load is more profound than pass number at the increment of friction force. Although CGP process results in reduction at the specific wear rate, the influence of the first pass is much higher than the subsequent ones. Furthermore, lower specific wear rate is occurred at the higher applied normal load. The scanning electron microscopy analyses indicated that the wear mechanism is transferred from adhesion, delamination, abrasion and oxidation for the annealed condition to abrasion and adhesion for the third pass CGP sample. Also, it is found that there is a reverse relationship between specific wear rate and hardness.

Three-factor response surface optimization of nano-emulsion formation using a microfluidizer.

Emulsification of sunflower oil in water by microfluidization was studied. Response surface methodology (RSM) and the central composite design (CCD) were applied to determine the effects of certain process parameters on performance of the apparatus for optimization of nano-emulsion fabrication. Influence of pressure, oil content and number of passes on the disruption of emulsions was studied. Quadratic multiple regression models were chosen for two available responses, namely Sauter mean diameter (SMD) and Polydispersity index (PdI). Analysis of variance (ANOVA) showed a high coefficient of determination (R(2)) value for both responses, confirming adjustment of the models with experimental data. The SMD and the PdI decreased as the pressure of emulsification increased from 408 to 762.3bar for the oil content of 5vol% and from 408 to 854.4bar for the oil content of 13vol%, and thereafter, increasing the pressure up to 952bar led to increasing the both responses. The results implied that laminar elongational flow is the alternative disruption mechanism in addition to inertia in turbulence flow, especially at low treatment pressures. Both of responses improved with increase in number of passes from 2 to 4cycles. The oil content depicted low effect on responses; however, interaction of this parameter with other regressors pointed remarkable impact. Also, the effect of pressure on Kolmogorov micro-scale was studied. The results implied that Kolmogorov equation did not take into account the over-processing and was applicable only for disruption of droplets in the inertial turbulent flow.