Types Of Serrations Research Articles

Comparative assessment between AlTiN and AlTiSiN coated carbide tools towards machinability improvement of AISI D6 steel in dry hard turning

AISI D6 (hardness 65 HRC) is one of the hard-to-cut steel alloys and commonly used in mould and die making industries. In general, CBN and PCBN tools are used for machining hardened steel but its higher cost makes the use for limited applications. However, the usefulness of carbide tool with selective coatings is the best substitute having comparable tool life, and in terms of cost is approximately one-tenth of CBN tool. The present study highlights a detailed analysis on machinability investigation of hardened AISI D6 alloy die steel using newly developed SPPP-AlTiSiN coated carbide tools in finish dry turning operation. In addition, a comparative assessment has been performed based on the effectiveness of cutting tool performance of nanocomposite coating of AlTiN deposited by hyperlox PVD technique and a coating of AlTiSiN deposited by scalable pulsed power plasma (SPPP) technique. The required number of machining trials under varied cutting conditions (speed, depth of cut, feed) were based on L16 orthogonal array design which investigated the crater wear, flank wear, surface roughness, chip morphology, and cutting force in hard turning. Out of the two cutting tools, newly-developed nanocomposite (SPPP-AlTiSiN) coated carbide tool promises an improved surface finish, minimum cutting force, longer tool life due to lower value of crater & flank wears, and considerable improvement in tool life (i.e., by 47.83%). At higher cutting speeds, the crater wear length and flank wear increases whereas the surface roughness, crater wear width and cutting force decreases. Chip morphology confirmed the formation of serrated type saw tooth chips.

Serrated yielding in austenitic stainless steels

ABSTRACT Austenitic stainless steels are widely employed in various applications due to many desirable properties such as excellent mechanical properties and corrosion/oxidation resistance. Serrated yielding phenomenon that occurs in austenitic stainless steels during deformation can cause significant changes in microstructures and mechanical properties. Thus, understanding the serrated yielding mechanisms and their influence on the mechanical behaviour on austenitic stainless steels is essential for developing and designing an advanced steel for harsher environment applications. In this article, a concise review of serrated yielding behaviour is examined and discussed with special attention to serration types, models describing the origin of the serrated flow, temperature-strain rate regimes for the serration occurrence, recent findings of the serration behaviour in a variety of austenitic steels and the role of dynamic strain ageing. Contradiction about the negative/beneficial impact of serrated flow on mechanical properties of newly developed austenitic stainless steels also is presented.

Study on serration flow and dynamic strain aging of Cr–Ti–B low-carbon steel

Compression tests were carried out for hot-rolled Cr–Ti–B low-carbon steels with different Cr contents (low Cr and high Cr) at three strain rates (0.01, 0.1 and 1 s−1) and temperatures ranging from 250 to 650 °C. The serrated flow and dynamic strain aging (DSA) behaviors during deformation were systematically analyzed. The results showed that the effect of the strain rate on serration flow is more obvious than that of the deformation temperature, and the serration type changes from type C to type A with increasing strain rate. The occurrence temperature range of DSA in high Cr steel (350–450 °C) is higher than that in low Cr steel (300–400 °C) at a strain rate of 1 s−1. The activation energy for DSA close to that for the diffusion of carbon, which is considered to produce DSA. A Cr–C cluster is observed in high Cr steel, which clarified that the delaying mechanism throughout the DSA regime is attributed to the pinning of carbon diffusion by Cr atoms.

Experimental Study of the Performance of a Propeller with Trailing-Edge Serrations

Experimental studies were conducted at a hemi-anechoic chamber to investigate the effectiveness of trailing-edge (TE) serration designs for reducing aerodynamic noise of a propeller. The propeller noise was measured under different speeds in both the vertical and horizontal directions. The thrust force produced by the propeller was also measured at rotational speeds. The flaplet, concave and sawtooth shapes of serration were integrated on the TE of baseline propeller to obtain three different serrated propellers. The results show that the flaplet, concave and sawtooth propellers improve the thrust force more than 10% on the basis of baseline propeller. Three types of TE serration all managed to attenuate large amount of noise, while the sawtooth serrations are more effective than flaplet and concave serrations in a wider frequency range. Then, the serration distribution length (DL) of sawtooth propeller was trimmed to other three different values to obtain the 3/4-DL, 1/2-DL and 1/4-DL propellers. The 3/4-DL propeller exhibited best comprehensive performance, by an average of 2.7 and 3.0 dB noise reduction in tested two positions and simultaneously generated overall 6.7% higher thrust force than did the baseline propeller. The morphological and parametric effects of TE serration in current studies are more significant in a relative high Reynolds number (1.4 × 106).

Portevin-Le Chatelier effect in austenitic steel Fe-18%Cr-8%Ni

The study of the mechanical behavior of the austenitic Fe-18% Cr-8% Ni steel was carried out in the temperature range of 530°C - 680°C at a strain rate of 1×10−3 s−1, as well as at a temperature of 620°C and strain rates of 1×10−2 s−1 - 1×10−4 s−1. At these conditions, the PLC effect was observed. Type A serrations were observed in the temperature range 530 - 680°C. A decrease in the strain rate at a temperature of 620°C leads to a change in the type of serrations from type A to type B.

체결력이 개선된 대형 트럭용 풀림방지 평행 세레이션 형태의 휠 볼트 설계에 관한 연구

To develop an anti-releasing wheel bolt for large trucks, the parallel serration (PS) type wheel bolt is introduced as an alternative for conventional saw blade (SB) type one. The forming load was analysed using FEM solver program according to the radius of curvature at the corner of serration top. The serration die for a PS type bolt which was designed with the possibly largest curvature radius (R) showed the lowest forming load at the top area of serration corner and PS type bolt die with R = 0.4 mm showed 1.6 times longer life cycle compared with SB type die. The PS type bolt revealed also higher clamping force and axial force compared with the SB type bolt.

A Review of the Serrated-Flow Phenomenon and Its Role in the Deformation Behavior of High-Entropy Alloys

High-entropy alloys (HEAs) are a novel class of alloys that have many desirable properties. The serrated flow that occurs in high-entropy alloys during mechanical deformation is an important phenomenon since it can lead to significant changes in the microstructure of the alloy. In this article, we review the recent findings on the serration behavior in a variety of high-entropy alloys. Relationships among the serrated flow behavior, composition, microstructure, and testing condition are explored. Importantly, the mechanical-testing type (compression/tension), testing temperature, applied strain rate, and serration type for certain high-entropy alloys are summarized. The literature reveals that the serrated flow can be affected by experimental conditions such as the strain rate and test temperature. Furthermore, this type of phenomenon has been successfully modeled and analyzed, using several different types of analytical methods, including the mean-field theory formalism and the complexity-analysis technique. Importantly, the results of the analyses show that the serrated flow in HEAs consists of complex dynamical behavior. It is anticipated that this review will provide some useful and clarifying information regarding the serrated-flow mechanisms in this material system. Finally, suggestions for future research directions in this field are proposed, such as the effects of irradiation, additives (such as C and Al), the presence of nanoparticles, and twinning on the serrated flow behavior in HEAs.

Fabrication and cutting performance of bionic micro-serrated scalpels based on the miscanthus leaves

The purpose of this study is to improve the cutting performance of the scalpel by imitating the micro-structures of miscanthus leaves. Four different types of micro-serrated edges were designed, and these micro-serrations were then successfully processed on the edges of the scalpels by laser induced plasma micromachining (LIPMM). Subsequently, cutting tests were carried out to explore the effect of micro-serrations on the cutting performance. Compared to the unprocessed commercial scalpel, the micro-serrated scalpels could significantly reduce the cutting force and actual cutting depth. The type of blended serration without spacing scalpel had the best performance during cutting soft tissue due to the induced serration effect, which was also verified by the cutting process images and finite element simulation.

Calculating the Pitch of a Serrated-Type Rotary Tiller

The high energy intensity associated with rotary tillage of soil serves as a deterrent for its widespread use. Rotary tillers are used in cases when there are no alternatives as to the soil quality, especially when machining hard and sod-covered soils. The authors have described new modernized rotary tillers of a serrated type and considered the optimal location of knives relative to the drum. ( Research purpose ) To determine the relationships for calculating the pitch of a serrated-type rotary tiller for soil preparation before potato planting. ( Materials and methods ) The authors have noted that currently, there are no methods for selecting the main parameters and operation modes of serrated-type rotary tillers. The research has proved that a new approach is required for selecting the working surface profile of the rotary tiller knife in order to reduce the energy consumption of tillage and improve its quality. The authors have used mathematical and graphical calculations to determine the optimal pitch of the tiller foot. ( Results and discussion ) The paper presents an expression for determining the amount of soil loosening during the operation of rotary tillers. It has been calculated that an increase in the tillage depth from 0.10 to 0.15 meters results in an increase in the pitch of a tiller foot from 0.04 to 0.06 meters and the optimal value is 0.05 meters. For approximate engineering calculations, it has been assumed that the optimal parameter of a foot pitch is 0.25-0.45 of the knife loading value. ( Conclusions ) It has been found that the number of knives in one section and the operating width of a knife do not affect the optimal tooth pitch. It has been determined that this indicator linearly depends on the depth of tillage: as it increases by 0.05 meters, the optimal foot step increases by 0.025 meters. It has been shown that as the working speed of the rotary tiller increases, specific energy consumption required for the treatment of a furrow slice decreases, and the efficiency of soil tillage improves.

Serrated flow and failure behaviors of a Hadfield steel at various strain rates under extensometer-measured strain control tensile load

A Hadfield steel has been investigated to clarify the serrated flow and to explore the failure behavior at room temperature. The tensile experiments were performed under extensometer-measured strain control, rather than under conventional cross-head displacement control, at strain rates ranging from 6 × 10−3 s−1 to 6 × 10−6 s−1. Three types of serrations, including type A, B and C ones, are observed. The occurrence of different types of serrations depends on both strain rate and strain level. The type C serration is identified in Hadfield steels at room temperature for the first time. At high strain rates, there is substantially higher serration density and reduction in stress compared with that observed at low strain rates. Furthermore, two different initiation modes of deformation bands are revealed. The fracture crack nucleates at a position with dense twins, and propagates primarily in the direction perpendicular to the tensile axis and deflects frequently due to the interaction with the boundary of grains and twins.

Analysis of Plastic Deformation Instabilities at Elevated Temperatures in Hot-Rolled Medium-Mn Steel.

The study addressed the microstructure and mechanical properties of hot-rolled advanced high-strength medium manganese steel. Some of the curves that were obtained in static tensile tests at deformation temperatures of 20–200 °C showed the occurrence of the heterogeneous plastic deformation phenomenon, called the Portevin-Le Chatelier (PLC) effect. The deformation temperature significantly influenced a serration character. The correlations between the deformation temperature, serration range, microstructural features, and fracture behavior were investigated. The curves showed no Lüders elongation as a result of the thermomechanical processing applied. The serrated flow phenomenon was observed at 60 and 140 °C. The serration type was different and the most enhanced at 140 °C, where the PLC effect was present in both uniform and post-uniform elongation ranges. The disappearance of serrations at 200 °C was related to the increased diffusion intensity.

Suppressing or promoting: The effect of coupled electron-heat field on serration behavior

Tensile tests under electric pulse were carried out on solid solution Al–Zn–Mg alloy. The obvious serration effect was found, including Lüders effect in yield stage and Portevin Le-Chatelier effect in plastic stage. For the Lüders effect, with the increase of current density, it first weakens and then strengthens, and the type of Lüders serrations changes from A to B (For type A, the serration is located above the envelope; for type B, the serration is around the envelope). When the current density is 5 A/mm2, the Lüders effect is the weakest. The Lüders effect under 55 A/mm2 is the strongest, which is stronger than that of non-pulsed condition. As for the effect of Portevin Le-Chatelier, it weakens continuously with the increase of current density, meanwhile, the type of Portevin Le-Chatelier serrations changes from B to C (For type C, the serration is located below the envelope). When the current density is 30 A/mm2, the type of Portevin Le-Chatelier serrations shows an obvious transition from B to C. The dislocation density is different when the two kinds of serration behavior occur. Combined with electroplastic, electromigration and dynamic strain aging theory, the influence of the electric pulse on the serration behavior was analyzed.

Experimental study on the mechanical strength and dynamic strain aging of Inconel 617 using small punch test

In the present work, the mechanical strength and deformation characteristics of Inconel 617 were studied using small punch test at different temperatures and deformation rates. As temperature increases, small punch characteristic parameters decreases and three temperature intervals are defined. An important conclusion here is that dynamic strain aging phenomenon can be found at a high-temperature small punch deformation of Inconel 617 in a multi-axial stress state. Due to serration plastic flow, small punch characteristic parameters of Inconel 617 appear no significant changes in the temperature range from 300 °C to 700 °C. To describe dynamic strain aging behaviour, serration type, critical displacement, and maximum load drop are discussed. As the temperature increases or deformation rate decreases, the serration type of the load–displacement curve gradually changes from Type A to Type C, and maximum load drop increases. Meanwhile, critical displacement displays normal and inverse behaviour at different temperature ranges. Based on the deformation characteristics analysis, the mechanical strength of Inconel 617 in different aging states was analysed. Finally, the relationship between the mechanical strength, small punch characteristic parameters and hardness was established. The results show that small punch test is an effective method for reasonably estimating the mechanical strength and dynamic-strain aging behaviour of Inconel 617.

A physically-based model considering dislocation–solute atom dynamic interactions for a nickel-based superalloy at intermediate temperatures

The uniaxial tensile tests are performed to study flow behavior of a nickel-based superalloy with different initial microstructures at an intermediate temperature range (473–973K). The experimental results show that the obvious serrated flow characteristics can be observed from the flow stress curves. Meanwhile, it is concluded that the occurrence of serrated flow features not only associate with deformation parameters, but also are prominently influenced by different initial microstructures. Furthermore, based on the plastic deformation mechanism of the investigated superalloy and dislocation-solute atoms dynamic interactions, a physically-based constitutive model is developed. The dynamic characteristics of the developed model are discussed, i.e., the evolution of moving dislocation, solute atoms concentration, and the strain rate dependent stress are analyzed. Additionally, various types of serrations are numerically simulated by appropriate parameters. Also, the predicted results show a good coincident with the observed data, suggesting that the established model can accurately describe the intermediate-temperature flow behaviors involving the serrated flow features of the investigated nickel-based superalloy.

Mechanical behavior and deformation mechanism of 7075 aluminum alloy under solution induced dynamic strain aging

In this study the mechanical behavior and deformation mechanism of 7075 aluminum alloy sheets under dynamic strain aging induced by solution treatment were investigated. The uniaxial tensile tests were carried out at various strain rates (8.33 × 10−5 s−1, 1.67 × 10−3 s−1, 3.33 × 10−2 s−1 and 1.33 × 10−1 s−1) for samples treated by different solution processes (solution for 30 min at temperatures of 573 K, 623 K, 673 K and 748 K, and then quenching). The Portevin-Le Chatelier (PLC) effect (i.e., serration types of stress-strain curves, strain rate sensitivity (SRS) and critical strain) were analyzed, causing changes in tensile strength, work hardening rate and elongation. The morphology, sizes and quantities of precipitates under different solution-quenching conditions were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the dissolution of secondary phase occurs during heat treatment, accompanied by coarsening behavior at lower temperatures, which leads to the transition characteristics of mechanical properties of the aluminum alloy in solid solution state. There exists a critical point of solution temperature (623K), namely, when the solution temperature is lower than this critical point, the microstructure after quenching is mainly composed of the matrix and secondary phase; otherwise it is mainly composed of solid solution. Therefore, the samples heated at different solution temperatures have different types of PLC effects. It is worth noting that the strong effect of dynamic strain aging induced at high solution temperature and low strain rate could simultaneously enhance the strength and toughness.

Microstructure, thermo-mechanical properties and Portevin-Le Chatelier effect in metastable β Ti-xMo alloys

The microstructure, mechanical properties and Portevin-Le Chatelier (PLC) effect in Ti-xMo alloys (x = 10, 12, 15 and 18 wt%), in the temperature range of 250–350 °C with strain rates from 10−3 s−1 to 10−4 s−1, are systematically investigated in tension by using transmission electron microscopy and Gleeble 3500 testing machine combined with a digital image correlation technique. Results show that Young modulus decreases with increasing Mo contents, which is related to a more stable β phase matrix and a decrease of ω phase fraction. Moreover, the values of Young modulus and 0.2% offset yield strength at elevated temperature are higher than the ones at room temperature in all the Ti-xMo alloys, except the Ti-18Mo alloy which shows an opposite result. These macroscopic features are consistent with the ω phase precipitation in deformed Ti-xMo alloys, due to the combined effects of ω phase strengthening and temperature softening. Furthermore, the serration type transforms from A to A + B, then to B and eventually to C as increasing temperature and decreasing strain rate as well as Mo contents, which mainly depends on the spatial cohesion of PLC bands influenced by the intensity of ω precipitate-dislocation interactions. Finally, the peak value of maximum stress drop magnitude appears in Ti-12Mo alloy and increases with decreasing the strain rate, which is attributed to a stronger intensity of ω precipitate-dislocation interactions caused by reducing dislocations movement and providing a longer ageing time for the precipitation of ω phase particles. Besides, the average stress drop magnitude increases in Ti-18Mo alloy and decreases in the other compositions as increasing engineering strain, which is related to the variation of ω phase fraction.

Effect of Various Knife Type, Cutting Angle and Speed on Cutting Force and Energy of Grape Cane

In this study, some cutting and energy properties of canes of local grapes varieties Okuzgozu (Vitis vinifera L. cv.) were determined depend on knife type, cutting angle and cutting speed during the spring pruning in 2018. The canes of grapes were obtained from a commercial farm in the Diyarbakir province. Cutting properties were measured by a material testing machine. According to test reslts, the significant differences were found between the knives types at 1 % probability level. The best results were determined at the flat knife knife type, followed by serrated 2 and serrated 1, respectively. While the lowest cutting force and cutting strength values were obtained at flat type (knife edge flat) as 234.50 N, 8.299 MPa, 1.783 J and 0.06307 Jmm -2 respectively, the highest values cutting forces, cutting strength, cutting energy and specific cutting energy were obtained at serrated type 1 (knife edge thin) knife as 303.8 N, 10.75 MPa, 2.136 J and 0.075610 J mm -2 respectively. The cutting force and energy values decreased with increasing knife-cutting angle from 0 ° to 40 ° . The maximum cutting force, cutting strength, cutting energy and specific cutting energy were observed at 0 ° cutting angle as 319.3 N, 11.30 MPa, 2.393 N and 0.08464 Jmm -2 respectively. T he effect of the knife loading speed on the cutting forces, cutting strength, cutting energy and specific cutting energy were found significant statistically (p<0.01). The lowest cutting force, cutting strength, cutting energy and specific cutting energy were obtained at the 1 m s -1 as 246.1 N, 8.705 MPa, 1.273 J and 0.04502 J mm -1 , respectively.

Effect of Deformation Temperature on the Portevin-Le Chatelier Effect in Medium-Mn Steel

Experimental investigations of the plastic instability phenomenon in a hot-rolled medium manganese steel were performed. The effects of tensile deformation in a temperature range of 20–140°C on the microstructure, mechanical properties, and flow stress serrations were analyzed. The Portevin–Le Chatelier (PLC) phenomenon was observed for the specimens deformed at 60 °C, 100 °C, and 140 °C. It was found that the deformation temperature substantially affects the type and intensity of serrations. The type of serration was changed at different deformation temperatures. The phenomenon was not observed at room temperature. The plastic instability occurring for the steel deformed at 60 °C was detected for lower strain levels than for the specimens deformed at 100 °C and 140 °C. The increase of the deformation temperature to 100 °C and 140 °C results in shifting the PLC effect to a post uniform deformation range. The complex issues related to the interaction of work hardening, the transformation induced plasticity (TRIP) effect, and the PLC effect stimulated by the deformation temperature were addressed.

Towards a greater understanding of serrated flows in an Al-containing high-entropy-based alloy

A serrated flow, which occurs in a material undergoing mechanical deformation, is a complex process of great engineering significance. Here statistical, dynamical, and multifractal modeling and analyses were performed on the stress-time series to characterize and model the stress-drop behavior of an Al0.5CoCrCuFeNi high-entropy alloy (HEA). Results indicate that the spatiotemporal dynamics of the serrated flow is affected by changes in the strain rate and test temperature. The sample entropy, in general, was found to be the highest in the samples tested at 500 °C. The higher complexity in the serrated flow at this temperature appeared to be associated with the stress-drop behavior that had intermediate values in terms of the maximum stress drop, the multifractality of the data set, and the histogram distributions. Moreover, the sample entropy was the lowest for the samples tested at 600 °C. The lower complexity values were associated with a wider multifractal spectrum and a less uniform and sparser distribution of the stress-drop magnitudes. In terms of the serration types, Type-C serrations were related to the lowest complexity values, widest multifractal spectra, and higher probability of exhibiting larger stress drops. Conversely, Type-A and B serrations were associated with the higher complexity, narrower spectra, and lower probability of higher stress drops. Furthermore, the body-centered-cubic (BCC) structure and the fully-ordered L12 nano-particles were found to emerge in the samples at 600 °C and are thought to be linked to the decreased spatiotemporal correlations in the stress-drop behavior.

Dynamic strain aging, deformation and fracture behaviour of the nickel base superalloy Inconel 617

Advanced Ultra Super Critical power plants (AUSC) with intended capabilities of higher efficiency and less emissions of CO2 compared with those of conventional power plants, require materials with high creep strength and good corrosion resistance. They are also required to withstand steam at high temperatures of 700–780 °C and pressures upto 35 MPa. Inconel 617 alloy is a candidate material for super heater and re-heater parts of boilers. In the present study, tensile behaviour of the Inconel 617 is investigated in the temperature range from RT to 900 °C at different strain rates from 5 × 10−4 s−1 to 1 × 10−2 s−1 and the deformed microstructures are characterised by optical and electron microscopy. Serrations are observed in the temperature range 300–700 °C at all the three strain rates which indicated the occurrence of dynamic strain aging (DSA). The amplitude of serrations increased with increase in the temperature and decrease in the strain rate. Temperature regime of DSA is confirmed to be from 300 °C to 700 °C by the occurrence of plateau in the yield strength, ductility minima and negative strain rate sensitivity in this regime. Activation energies for the serrated flow are found to be 65, 80 and 110 kJ/mol for the three types of serrations, namely B, (A+B) and C respectively. The controlling mechanism of the DSA is found to be diffusion of carbon through dislocation cores in the lower temperature range and diffusion of substitutional elements Cr and Mo in the higher temperature range. TEM studies revealed increase in the number of slip bands as well as interaction of dislocations with solute atoms with increase in the temperature up to 700 °C. Precipitation of carbides and subgrain formation was observed at 700 °C, at the ductility minima. SEM examination of the fracture surfaces revealed ductile fracture with dimples and facets at room temperature, ductile fracture with essentially dimples at 400–600 °C, at intense serrations in the flow curve. At 700 °C, at ductility minima, there was mixed mode of fracture with dimples, facets and intergranular cracks associated with some grains boundaries. At 800 °C and 900 °C, there was completely ductile fracture with large and deep dimples.