Bulk Deformation Processes Research Articles

Squeeze casting for metal alloys and composites: An overview of influence of process parameters on mechanical properties and microstructure

Squeeze casting is a well-established and reliable process for fabricating high-integrity metallic alloys, bimetals, and composites. The quality and high performance of squeeze cast components are dependent on optimum casting conditions. Inappropriate selection of parameter values may adversely affect the quality of the casting. The squeeze cast components are generally subjected to secondary processing such as heat treatment, extrusion, and other bulk deformation processes to improve the microstructural features and mechanical properties. Heat treatment further refines the grains and reduces porosity, consequently improving tensile strength, and hardness; however, ductility decreases. This paper provides a comprehensive review on studies concerning the influence of processing parameters on porosity, density, percentage elongation, strength, hardness, wear, and fracture of squeeze casting alloys, aiming to provide sufficient information on the squeeze casting process and the effects of processing parameters on product quality.

Experimental Investigation on the Effect of Electrically Assisted Rapid Heating in Bulk Metal Forming

Many industries utilize hot metal forming to reduce forming forces and material flow issues. In this study, electrically assisted (EA) rapid heating is used in direct comparison to conventional heating methods. Three materials were investigated: AISI 4340, Al-7075-T6, and Ti-6Al-4V. Samples were heated at an approximate rate of 100 °C/s before applying compressive loads, simulating forging or other bulk deformation processes. Afterwards, samples were prepared for further microstructure evaluation. It was observed that high-rate temperature increase resulted in some developments in the microstructure and phases, as seen in AISI 4330, for example. Additionally, the effect of electricity was noticed to have a significant impact on flow stresses, as observed in many of the compression tests, immediately following the rapid heating process. Experiments and images from optical microscopy show that samples experienced drastic and immediate decrease in flow stress at all temperatures when using the EA rapid heating method versus the conventional method with seemingly no change to the material microstructure. This may be explained by the lack of phase changes at lower temperatures combined with the effect of electricity. Further investigation into the changes in micro-porosity, intermetallic phases, and changes in precipitates are suggested to supplement the current understanding of the drastic stress drop caused by passing electrical currents through metals.

Review: titanium–titanium boride composites

Titanium in situ reinforced with titanium boride (TiBw) has garnered significant attention as one of the most promising titanium composites today. A significant number of processing approaches have been reported on the fabrication of these unique composites. This brief review provides an update on recent activities within the area focusing largely on research conducted over the past 5 years. Approaches discussed include bulk deformation processes such as rolling, 2D forging, equal channel angular pressing, (laser and non-laser-based) additive manufacturing, and new microstructural designs implemented for this composite system. Moreover, the potential of this composite as a biomaterial is also discussed.

Modelling challenges for incremental bulk processes despite advances in simulation technology: example issues and approaches

Abstract Incremental bulk deformation processes have traditionally been difficult to simulate. This paper will argue that, despite advances in computation and software, they remain difficult to model. The main reason for this is the shortage of ideas on what is the real objective of FE modelling for such processes. Even a very detailed model and data obtained in simulation does not give answers to the main question - how to optimise the process parameters? High computational time and volume of information only aggravate the situation. All modern mathematical techniques of dimensionality reduction (such as POD/PGD) lose their power when the priorities and acceptable compromises of modelling are not clear. This paper tries to use a large volume of available experimental and modelling experience to illustrate this problem and look for possible break-through directions.

Monitoring Tensile Fatigue of Superelastic NiTi Wire in Liquids by Electrochemical Potential

Fatigue of superelastic NiTi wires was investigated by cyclic tension in simulated biofluid. The state of the surface of the fatigued NiTi wire was monitored by following the evolution of the electrochemical open circuit potential (OCP) together with macroscopic stresses and strains. The ceramic TiO2 oxide layer on the NiTi wire surface cannot withstand the large transformation strain and fractures in the first cycle. Based on the analysis of the results of in situ OCP experiments and SEM observation of cracks, it is claimed that the cycled wire surface develops mechanochemical reactions at the NiTi/liquid interface leading to cumulative generation of hydrogen, uptake of the hydrogen by the NiTi matrix, local loss of the matrix strength, crack transfer into the NiTi matrix, accelerated crack growth, and ultimately to the brittle fracture of the wire. Fatigue degradation is thus claimed to originate from the mechanochemical processes occurring at the excessively deforming surface not from the accumulation of defects due to energy dissipative bulk deformation processes. Ironically, combination of the two exciting properties of NiTi—superelasticity due to martensitic transformation and biocompatibility due to the protective TiO2 surface oxide layer—leads to excessive fatigue damage during cyclic mechanical loading in biofluids.

Experimental-assisted design development for an octahedral cellular structure using additive manufacturing

Purpose – This paper aims to demonstrate the design and verification of a 3D reticulate octahedral cellular structure using both analytical modeling and additive manufacturing. Traditionally, it has been difficult to develop and verify designs for 3D cellular structures due to their design complexity. Design/methodology/approach – Unit cell modeling approach was used to model the octahedral cellular structure. By applying structural symmetry simplification, the cellular structure was simplified into a representative geometry that could be further designed with a standard beam theory. The verification samples were fabricated with EBM process using Ti6Al4V as materials, and compressive testing were performed to evaluate their properties. In addition, designs with different number of unit cells were investigated to evaluate their size effect. Findings – Explicit mechanical property design (including modulus and compressive strength) of the octahedral cellular structure was realized via parametric equations driven by geometrical designs and material types. In addition, it was verified both numerically and experimentally that the octahedral cellular structure exhibit unusual size effect, which is highly predictable. Unlike some of the other cellular structures, the octahedral cellular structure exhibits softening behavior when the number of unit cell increases between the sandwich skins, which could be explained by the upsetting effect commonly observed in bulk deformation processes. Originality/value – This paper established a more comprehensive understanding in the design of octahedral cellular structures, which could enable this type of structure to be designed for sandwich structures with higher fidelity. Therefore, this study not only demonstrated an efficient methodology to design 3D cellular structures using additive manufacturing, but also facilitated the development of design for an additive manufacturing theory.

On materials flow using different lubricants in upsetting process

Purpose – The purpose of this paper is to apply the upsetting process to cylindrical specimens using flat end dies in which three types of lubricants were used. In many industrial processes, friction and lubrication have major advantages and are key during the metal forming process. Upset forging is a process which increases the diameter of the work-piece by compressing its length. Design/methodology/approach – The materials flow for various materials using different lubricants in upsetting was investigated in this study. AISI 304 austenitic-stainless steel and commercially pure aluminium (Al99.7) were used as the test materials. The upsetting process was applied to the cylindrical specimens using flat end dies. Three types of lubricants, namely, grease, graphite and SAE 40 oil, were used in this study. Experiments were performed using a hydraulic press, which has 5 mm/s ram speed, with a capacity of 150 metric tons. On the other hand, finite element methods (FEMs) have been carried out to analyse the forming performance for displacement prediction in the barrelling process. Findings – The results showed that the measured radius of the curvature of the barrel seemed to confirm the calculation values used before the initiation of the experimental process. It has been observed that the surface roughness had no considerable effect on the barrelling contour changes on the free surfaces, as it showed an increasing deformation ratio for all materials and lubricant types. However, minimum friction at the interface seems to occur with the grease lubricant. The present analyses show that FEMs, which can be used in the rapid prediction of required barrelling process displacements, are more suitable for use in a pressure distribution analysis for the development of the barrelling radius. Research limitations/implications – It would be interesting to search the material flow for more different materials and lubricants. It could be a good idea if future work could be concentrated on the material flow on upsetting by using different lubricants. Practical implications – Open-die forging, which is also known as the upsetting process, is one of the simplest forging operations used in bulk deformation processes. This operation can be explained as a solid work-piece which is positioned between two flat dies, and then with the aid of compression, the height of the work-piece is reduced under controlled working parameters during the upsetting process, in which friction and surface roughness are the major parameters playing an important role on the material flow. In a cold upsetting process, one of the undesirable conditions is that barrelling occurs as a consequence of friction between the work-piece and the die surfaces. The existence of this frictional constraint directly affects the plastic deformation of the work-piece, as friction causes barrelling in upsetting processes. However, it has been observed that the use of lubricants reduces the degree of bulging. Social implications – This paper will be useful for industrial applications. Originality/value – The main value of this paper is to contribute and fulfil in detail the material flow of various materials using different lubricants that are being studied so far in the literature.

Re-equilibration of natural H2O–CO2–salt-rich fluid inclusions in quartz—Part 1: experiments in pure water at constant pressures and differential pressures at 600 °C

Re-equilibration processes of natural H2O–CO2–NaCl-rich fluid inclusions quartz are experimentally studied by exposing the samples to a pure H2O external fluid at 600 °C. Experimental conditions are selected at nearly constant pressure conditions (309 MPa) between fluid inclusions and pore fluid, with only fugacity gradients in H2O and CO2, and at differential pressure conditions (394–398 MPa, corresponding to an internal under-pressure) in addition to similar CO2 fugacity gradients and larger H2O fugacity gradients. Modifications of fluid inclusion composition and density are monitored with changes in ice dissolution temperature, clathrate dissolution temperature and volume fraction of the vapour phase at room temperature. Specific modification of these parameters can be assigned to specific processes, such as preferential loss/gain of H2O and CO2, or changes in total volume. A combination of these parameters can clearly distinguish between modifications according to bulk diffusion or deformation processes. Bulk diffusion of CO2 according to fugacity gradients is demonstrated at constant pressure conditions. The estimated preferential loss of H2O is not in accordance with those gradients in both constant pressure and differential pressure experiments. The development of deformation halos in quartz around fluid inclusions that are either under-pressurized or over-pressurized promotes absorption of H2O from the inclusions and inhibits bulk diffusion according to the applied fugacity gradients.

Mechanisms of Creep Deformation in Pure Sn Solder Joints

The work reported here concerns the creep of pure Sn solder joints with Cu metallization (Cu||Sn||Cu). Steady-state creep tests in shear are combined with electron backscatter diffraction (EBSD) analysis of the evolution of the microstructure during creep to clarify the deformation mechanism and the nature of the microstructural evolution. The creep behavior of the joint changes significantly with temperature. At low temperature (65°C), two distinct creep mechanisms are observed. Low-stress creep is apparently dominated by grain boundary sliding, as evidenced by the low stress exponent (n ≈ 4), low activation energy (Q ≈ 42 kJ/mole), and significant grain rotation during creep. High-stress creep is dominated by bulk deformation processes, evidenced by a high stress exponent (n ≈ 9), an activation energy like that for bulk diffusion (Q ≈ 70 kJ/mole), and a relatively fixed microstructure. At high temperature all aspects of its behavior are consistent with deformation by bulk creep mechanisms; the stress exponent and activation energy are high (n ≈ 5 to 7, Q ≈ 96 kJ/mole), and despite significant grain coarsening, the microstructure retains (and strengthens) a fixed [001] texture. The results suggest that a “segmented” constitutive equation of Dorn type is most suitable for the low-temperature behavior, while a “hyperbolic” constitutive equation may be preferable at high temperature.

Microstructure Evolutions during the Hot Extrusion Process of AZ 31B Magnesium Alloy

The hot bulk deformation processes (such as extrusion, forging and rolling) are efficient ways to produce fine microstructure. The effects of extrusion parameters on the evolved microstructure of directly extruded AZ 31B magnesium alloy were investigated. Extrusion processes were carried out at five different combinations with ram speed ranging from 2 to 8 mm·s–1 and billet temperature ranging from 350 to 450 ℃. The experimental results show that the peak extrusion force decreases with increase in billet temperature and decreases in ram speed. During all the extrusion the profile temperature and die temperature rise continuously. Small particles of secondary phase (β-Mg17Al12) are uniformly distributed near the edge of the extruded profiles whereas their distribution is nonuniform in the centre of the extrudates. The size of secondary phase particles present in the central region of the specimens was found to increase with billet temperature and extrusion speed. All the specimens showed mixed microstructure―In the central region of the specimen, low volume fraction of dynamically recrystallized fine grains presented at the grain boundaries of original coarse grains; but near the edge region, the microstructure consisted nearly equiaxed fine recrystallized grains.

Scaling of fracture energy in tensile debonding of viscoelastic films

The work done to separate viscoelastic adherends is often dominated by energy dissipation due to the bulk deformation that accompanies the intrinsic processes of interfacial separation. The inter-relationship between bulk and interfacial deformation processes is studied here by analyzing a one-dimensional model for steady-state crack propagation between a rigid substrate and a thin viscoelastic film when the latter is subjected to tensile loading and the former is fixed. The viscoelastic layer is represented by a standard linear solid and is connected to the rigid substrate via a Dugdale cohesive zone model. The principal result of the analysis is a prediction for the dependence of the total work of fracture on the rate of loading. A threshold crack-tip velocity that governs the onset of dissipation is determined as a function of the film thickness and the interfacial and viscoelastic parameters of the film. Based on the ratio of the crack-tip velocity to the threshold velocity, three velocity regimes are identified where the energy dissipation is low, high, or intermediate. These correspond, respectively, to the overlap of the cohesive zone with the film material that is completely relaxed, is completely unrelaxed, or is in the process of relaxation. An approximate solution for the scaling of fracture energy in these three regimes has been presented. Finally, the relevance of these results to a two-dimensional problem is discussed.

Finite element modelling and simulation of bulk material forming

PurposeTo provide a selective bibliography for researchers working with bulk material forming (specifically the forging, rolling, extrusion and drawing processes) with sources which can help them to be up‐to‐date.Design/methodology/approachA range of published (1996‐2005) works, which aims to provide theoretical as well as practical information on the material processing namely bulk material forming. Bulk deformation processes used in practice change the shape of the workpiece by plastic deformations under forces applied by tools and dies.FindingsProvides information about each source, indicating what can be found there. Listed references contain journal papers, conference proceedings and theses/dissertations on the subject.Research limitations/implicationsIt is an exhaustive list of papers (1,693 references are listed) but some papers may be omitted. The emphasis is to present papers written in English language. Sheet material forming processes are not included.Practical implicationsA very useful source of information for theoretical and practical researchers in computational material forming as well as in academia or for those who have recently obtained a position in this field.Originality/valueThere are not many bibliographies published in this field of engineering. This paper offers help to experts and individuals interested in computational analyses and simulations of material forming processes.

UBET-Based Numerical Modeling of Bulk Deformation Processes

The paper summarizes the development of numerical procedures for modeling bulk deformation process and preform designing techniques based on the upper bound elemental technique (UBET). UBET has a unique place where an approximate, but faster solution is needed for decision making. In designing and optimizing multistage forging and profile ring-rolling processes, an approximate solution can be used to identify the most influential process parameters. Once an optimum combination of process conditions are determined, computationally intensive, but more accurate finite element analysis can be used to verify and refine results. In this paper, UBET procedures for closed-die forging and profile ring rolling are high-lighted. Experimental investigations are used to validate the model predictions. Also, the UBET-based preform design tool is presented as a process and die design tool for multistage forging processes. Application of these techniques is presented with evidence of effective material usage and extended overall die-life.

Grain Refining of Magnesium Alloy AZ 31 by Equal Channel Angular Extrusion

Among the conventional and alleged bulk deformation processes in metalworking, equal channel angular extrusion (ECAE) is an innovative and attractive method to refine grain structures effectively. Grain refining by this process on magnesium alloy AZ31 was studied and compared to published data. An interesting and unique question is proposed and studied - that is, how dominant is the accumulated strain as obtained through multiple angular extrusion passes. Tensile tests were performed at room and high temperatures, and processed AZ31 was examined with optical and transmission electron microscopy as well as x-ray diffraction.

Instability criteria for hot deformation of materials

Forming and forging processes are among the oldest and most important materials related technologies. New materials technologies centre on the development and widespread use of thermomechanical processing, particularly for aerospace alloys and concepts of metal workability and formability. Workability refers to the relative ease with which a metal can be shaped through plastic deformation. The term workability is often used interchangeably with the term formability, which is preferred for the shaping of sheet metal parts. However, workability is usually used to refer to the shaping of materials by such bulk deformation processes as forging, extrusion, and rolling. The characterisation of mechanical behaviour of a material by tension testing measures two different types of mechanical property: strength properties (such as yield strength and ultimate tensile strength) and ductility properties (such as percentage elongation and reduction in area). Similarly, the evaluation of workability involves both the measurement of the resistance to deformation (strength) and determination of the extent of possible plastic deformation before fracture (ductility). Therefore, a complete description of the workability of a material is specified by its flow stress dependence on processing variables (for example strain, strain rate, preheat temperature, and die temperature), its failure behaviour, and the metallurgical transformations that characterise the alloy system to which it belongs. However, the major emphasis in workability is on measurement and prediction of limit of deformation before fracture. Therefore, the emphasis in the present review article is on methods for determining the extent of deformation a metal can withstand before cracking or fracture occurs. Flow stress data are essential in the development of constitutive equations and processing maps. One of the requirements for process modelling is a knowledge of the material flow behaviour for defining the deformation maps that delineate ‘safe’ and ‘non-safe’ hot working conditions. These maps show in the processing space (that is on axes of temperature T and strain rate ɛ·) the processing conditions for stable and unstable deformation. The range of T and ɛ· for stable material flow useful in the development of process control algorithms should be obtained from physical quantities, which can be evaluated from the test data. As such there is no unique instability theory existing to delineate the regions of unstable flow during hot deformation which is applicable for all the materials. The designer has to establish a suitable theory on the basis of microstructural observations of the flow localisation in the intended materials. Various existing theories are reviewed for identification of flow instabilities (such as adiabatic shear banding, intercrystalline cracking, prior particle boundary cracking in powder compacts, wedge cracking) during hot deformation of materials, and these theories are verified by considering the flow stress data of IN 718 and the reported microstructural observations from different sources.

Determination of the workability of clays using the upset test

In ceramic industry, workability (or plasticity) is generally defined as the product of yield stress and maximum deformation without fracture. In the present study, yield point values for two clay bodies have been obtained from compression tests done without friction at the die contact surface. Maximum deformations to fracture, on the other hand, have been determined from local strain measurements of bulget surfaces of cylinders compressed with friction at the die contact surface. Workability indexes have been obtained from the products of yield stresses and maximum deformations. For both clay bodies studied, yield values decreased and amount of maximum deformation increased with increasing water content. Thus, the workability index showed a maximum determining the optimum water content. Forming limit line (FLL) technique, based on local strain measurements on the bulget surfaces of cylinders upset with friction at the die contact surface, form the basis for evaluating the workability of metals as a function of material variables. It also forms the basis for the analysis of workability in bulk deformation processes of metallic materials. In the present case, the FLL technique has been applied to ceramic bodies in determining their maximum deformation to fracture and a new easy-to-apply technique not necessitating the use of special equipment, has been developed for the determination of workability of ceramic bodies.

MeV ion irradiation-induced creation and relaxation of mechanical stress in silica

In situ wafer curvature measurements were performed to study mechanical stress in amorphous SiO2 during Xe, Ne, and Er ion irradiation at energies in the 0.27–4.0 MeV range. Three phenomena are observed: network compaction, radiation-induced viscous flow, and a nonsaturating anisotropic deformation phenomenon. The radiation-induced viscosity is shown to be inversely proportional to the energy density deposited into atomic displacements. The relation between radiation-induced flow and diffusion is discussed in the context of the Stokes–Einstein relation. Viscous flow serves to relax stress, yet a continuous nonsaturating anisotropic deformation effect causes the stress in the irradiated layer to saturate at nonzero values: Xe irradiation at an energy below 3.6 MeV results in a tensile saturation stress; for higher energies a compressive stress builds up. These effects are explained in terms of competing bulk and surface deformation processes resulting from local heating of the SiO2 around the ion tracks. The macroscopic effect of deformation phenomena is illustrated by showing the surface morphology after 4.9 MeV Er irradiation of silica through a contact implantation mask. Finally, an in situ stress study of an alkali borosilicate glass is presented. In this case a fourth radiation induced effect is observed, namely, the generation and annihilation of volume occupying point defects. These defects are shown to anneal out at room temperature, following a broad spectrum of activation energies.

Metalworking science and engineering

Part I: Classification of Materials Processes and Technical Background. Scope and Classification of Materials Processes. Fundamentals of Elasticity and Plasticity. Stress-Strain Curves and Related Mechanical Properties and Related Phenomena. Methods for Analyzing Metalworking Processes. Part II: Classification of Metalworking Processes and Massive or Bulk Deformation Processes. Classification of Metalworking or Metalforming Processes. Rolling. Drawing, Extrusion, and Allied Processes. Classification of Forging Processes and Open-Die Forging. Closed-Die Forging Processes and Related Operations. Analysis, Classification, and Shearing, bending, and Stretch-Forming Operations. Deep Drawing Considerations and Evaluation of Formality. CAD/CAM of Sheetmetal Drawing.

Metal Formability in Bulk Deformation Processes

Brief consideration is given to several mechanical tests for the measurement of metal formability. The compression test is considered in some detail, and its usefulness in the calculation of forming limit lines and as a source of information on the feasibility of forming processes is demonstrated.

Determination of the flow stress-strain curves for metals from axisymmetric upsetting

A new test method has been developed for determining flow stress-strain curves of materials used in bulk deformation processes such as extrusion, forging and croping. These curves are of vital importance in the industry. The test piece is made of a 14 mm diameter, 21 mm height cylinder which is deformed between two flat dies. The maximum height reduction is chosen to reproduce the maximum strain and strain rate required for the process. The stress-strain curve is plotted by using the values of forging load, height reduction and maximuu diameter-minimum diameter ratio of the deformed cylinder. This so-called shape ratio is found to correspond perfectly to the friction shear stress between the cylinder and the dies. Experiments have been performed on 1% carbide steel samples at room temperature, where the results have demonstrated the accuracy of the test for determining the stress-strain relationship under the friction conditions generally observed between the cylinder and the dies. The proposed test can be carried out on any simple press using a pair of flat dies. This very simple tooling may be accomodated in production equipment in order to obtain accurate results concerning stress-strain relationship at the relevant strain rate and temperature.