High Performance PM Research Articles

Design and analysis of a hybrid permanent magnet variable leakage flux motor for low core loss and wide speed range

In this paper, a new hybrid permanent magnet variable leakage flux (VLF-HPM) motor is proposed. In order to enhance motor speed range, short arc-shaped and elliptical-shaped magnetic barriers are placed on the q-axis magnet circuit, realizing the so-called leakage flux effect. In addition, ferrite PMs are artfully designed, so self-leakage flux can be reduced while main flux is enhanced. The relationship among PM topology, flux barrier and flux-regulation capability are also investigated in detail. Finally, the electromagnetic performance of VLF-HPM motor is evaluated by the finite element analysis and compared with a conventional V-typed PM motor. It is noted that, compared with conventional V-typed PM motor, the VLF-HPM motor possesses lower core losses and a wider speed range, which offers a new research path for high-performance PM motor.

The designed high-performance PM Ti-6Al-4V alloy via two-step pressureless sintering

Sintering is a critical step to obtain the desired mechanical properties for titanium alloys. However, the residual porosity and the coarse microstructure caused by traditional pressureless sintering adversely affect the mechanical properties. Herein, we proposed a novel two-step pressureless sintering route to achieve sintering densification and grain refinement. The high density of 99.0% and the refined parent β grains with a size of 90.57 µm for Ti-6Al-4V alloy are acquired ultimately, which is among the best pressureless sintering practice reported in the literatures. The selection of two-sintering temperature (< 1250 °C) is confirmed to be the key to improving density and reducing grain size. Benefitting from grain refinement, the increased number of grain boundaries provides more channels for vacancy diffusion, and the formation of small α colonies with multiple orientations makes the Widmanstätten microstructure more uniform. During plastic deformation, the abundant dislocation cross slips and nanoscale twins of face-centered cubic phase within these colonies relieve the stress accumulation of phase interfaces, thereby delaying the formation of cracks and promoting the large plastic flow with the high-stress level. Compared with standard sintering, two-step sintered samples exhibit better mechanical properties (ultimate tensile strength of 968 MPa, yield strength of 871 MPa and elongation of 16.1%), achieving the strength-ductility synergy. This work casts light on developing high-performance and low-cost titanium and its alloys.

Phase matching achieved by isomorphous substitution in IR nonlinear optical material Ba2SnSSi2O7with an undiscovered [SnO4S] functional motif

A new paradigm for designing high-performance PM NLO crystals: a novel PM fresnoite oxychalcogenide, Ba2SnSSi2O7, has been successfully designed and obtained by the isomorphous substitution strategy, on the basis of the NPM parent Ba2TiOSi2O7.

Development of a High-Performance Axial Flux PM Machine With SMC Cores for Electric Vehicle Application

A new axial flux permanent magnet machine (AFPM) with soft magnetic composited (SMC) cores is proposed for electric vehicle (EV) application in this paper. As its windings are wound on the stator ring core, it can be regarded as a toroidally wound internal stator (TORUS) machine. With the adopted SMC material for stator core, this machine has the benefits of 3-D magnetic flux properties. The windings and SMC cores can be designed to form a very compact structure, and thus, the torque density can be improved greatly. To obtain the a good flux concentrating ability, two TORUS machines are designed and analyzed, one is with NdFeB magnet for high-performance EV application and the other is with the cheap ferrite magnet for low-cost application. The 3-D finite-element method is used to analyze the electromagnetic parameter and performance. For performance comparison, a commercial AFPM with yokeless and segmented armature P400 is used.

Design and analysis of a high-performance dual-rotor PM synchronous reluctance machine with toroidal windings

This paper presents a dual-rotor permanent magnet synchronous reluctance machine (PM-SynRM) with toroidal windings to improve the magnetic torque and the utilization of two torque components, thus to obtain high electromagnetic performance, such as torque, efficiency, and power factor. To highlight the advantages of the proposed dual-rotor PM-SynRM, all of its machine characteristics, including airgap flux density, back electromotive force (EMF), torque, power, efficiency, and flux weakening capability are compared to those of a conventional PM assisted SynRM (PMA-SynRM) with the same machine size and operating conditions, with the aid of a finite element method (FEM) using the JMAG-Designer. Furthermore, the proposed dual-rotor PM-SynRM is verified to have superior endurance against the magnet irreversible demagnetization within five times of the rated current excitation.

Mechanical performance of Cr-alloyed PM steel after different sintering and heat treatment operations

Main benefits of the PM technology versus conventional steel making processes in the manufacture of structural steel parts are high material utilization, low energy consumption and short production time. These benefits are fully exploited by choosing the right combination of material and processing route to get the required mechanical properties at a low production cost. Powder grades pre-alloyed with Cr are robust and cost effective materials which are suitable for high performance PM steel components. This paper presents mechanical properties of Cr-alloyed PM steel obtained after different processing routes, including high temperature sintering, sinter-hardening and heat treatment by low pressure carburizing. Static mechanical data are presented as well as results from plane bending fatigue tests. Microstructures are also shown and correlated with the mechanical properties obtained for the respective processing routes.

高性能銅系焼結部品用原料粉末の開発

高性能銅系焼結部品用原料粉末の開発

Development of Novel Pre-alloyed PM Steels for Optimization of Machinability and Fatigue Resistance of PM Components

It is well known that a large proportion of ferrous PM components require secondary machining operations for dimensional conformance or for producing geometrical features that cannot be generated during die compaction. Nevertheless, the machining behavior of PM parts is generally characterized as being “difficult” due to the presence of residual porosity that lowers thermal conductivity and induces interrupted cutting. Several admixed additives such as MnS and BN-h can be used to improve the machining behavior of PM steels. Nevertheless, their negative effect on mechanical properties, especially fatigue resistance, makes their utilization uninteresting for the fabrication of high-performance PM steel components. This article summarizes the work carried out to develop a novel PM steel that was especially engineered to form machinability enhancing precipitates. This new material is pre-alloyed with tin (Sn) in order to form Cu-Sn (Cu(α)) precipitates during transient liquid phase sintering. The newly developed material presents machinability improvement of 165% compared to reference material used in the PM industry as well as increases in toughness and fatigue resistance of 100% and 13%, respectively.

Effects of annealing on high velocity compaction behavior and mechanical properties of iron-base PM alloy

High performance PM iron-base alloy was fabricated with annealed powder by high velocity compaction. The effects of powder annealing on densification behavior, variations of stress waves and the resulting mechanical properties of iron-base alloy were studied. The results show that micro-hardness of the powder decreases from 97Hv to 81Hv after annealing at 800°C, facilitating the improvement of powder plasticity and compressibility. Compared with the compacts prepared from unannealed alloy powder, green density of the compacts made from annealed alloy powder is 0.11–0.25g/cm3 higher at the impact velocity range of 6.2–9.4m/s. Green density of the compact made from annealed alloy powder is as high as 7.61g/cm3 at 9.4m/s. The tensile strength, yield strength and hardness of the heat treated specimen reach 1459MPa, 1185MPa and 50.2HRC, respectively.

Review and Analysis of Powder Prior Boundary (PPB) Formation in Powder Metallurgy Processes for Nickel-based Super Alloys

Powder metallurgy of nickel-based super alloys have been developed and used for a wide range of products, owing to their excellent high temperature rupture life, creep strength and fatigue crack growth resistance. Typical processes for high performance PM super alloys include hot isostatic pressing (HIPing), hot extrusion and hot isothermal forging. Hot isostatic pressing is normally conducted at a high temperature by using metal forming standards at low pressure for a long time. However an intrinsic problem, i. e. powder prior boundary (PPB) precipitate networks, can occur in the HIPing process. In this paper, a comprehensive review of PPB formation in the powder metallurgy of super alloys is presented. Research on PPB formation process from room temperature to high temperature and during HIPing, has been reviewed and PPB formation mechanisms are discussed. Methods to reduce PPB effects on the mechanical properties of nickel-based super alloys, including heat treatment, changing the proportions of composition elements, and plastic deformation to break up the PPB networks, are reviewed.

Power Inverter Based Comparison of Torque Ripple Suppression in IPMSM with Concentrated Winding

This study compares the characteristics of a PWM voltage source inverter (VSI) and PWM current source inverter (CSI) for an IPMSM drive system with concentrated winding. Past analysis showed that the PWM CSI had inferior operating characteristics compared with the PWM VSI. Thus, high-performance PM motor drive systems have been using a VSI for small-capacity applications. There has been almost no research addressing improvements in CSI motor drive systems. In this study, experiments were performed to compare the three-phase current and torque characteristics generated by VSIs and CSIs.

From Sintered Iron to High Performance PM Steels

Since low alloyed sintered steels were introduced in the market of the structural parts, we have followed the evolution of a material with poor mechanical properties and any uniformity (in the sense of reproducibility) to materials that today are produced with high reliability and performance. The working efficiency could be equivalent in many cases with the best wrought steel, and maintaining a good margin in terms of cost and competitively. In this paper a complete review of the topic is accomplished, from the early times when the first parts were made by plain iron or iron-carbon, going through the different alloying systems: Fe-Cu, Fe-P, Fe-Cu-Ni-Mo, and more recently Fe-Cr-Mo and Fe-Mn. The development in processing routes has been considered too. The main milestones in the field of new alloying systems have been: 1) the introduction of Cu in 60-70’s, 2) the new complex systems with Cu-Ni-Mo in the 80’s and 3) the introduction of alloying elements with high oxygen affinity (in the late 90’s). Regarding the milestones in processing could be considered: 1) the development of new mixing procedures, 2) the warm compaction and high velocity compaction, 3) the improvements in sintering control and high temperature sintering. Several decades of research and innovation, acting on the processing system (mixing, pressing, sintering, post-sintering operations,…) and on the alloying system (from the earliest times with plain iron to complex systems used today), has allowed us to have a highly competitive materials, in terms of performance, and processes in terms of cost. The future is still open to new developments.

Bonding evolution with sintering temperature in low alloyed steels with chromium

At present, high performance PM steels for automotive applications follow a processing route that comprises die compaction of water-atomized powder, followed by sintering and secondary treatments, and finishing operations. This study examines Cr-alloyed sintered steels with two level of alloying. In chromium-alloyed steels, the surface oxide on the powder is of critical importance for developing the bonding between the particles during sintering. Reduction of this oxide depends mainly on three factors: temperature, dew point of the atmosphere, and carbothermic reduction provided by the added graphite. The transformation of the initial surface oxide evolves sequence as temperature increases during sintering, depending on the oxide composition. Carbothermic reduction is supposed to be the controlling mechanism, even when sintering in hydrogen-containing atmospheres. The effect of carbothermic reduction can be monitored by investigating the behavior of the specimens under tensile testing, and studying the resultant fracture surfaces.

Powder metallurgy steels for highly loaded precision parts

Ferrous powder metallurgy precision components are increasingly being used for highly loaded applications. This requires consistent improvement in materials properties without sacrificing geometrical precision. Here, the various approaches for obtaining this goal are discussed. The relationships between density/porosity and properties, especially fatigue, are described, as is the effect of higher sintering temperatures. The resulting requirements towards equipment are discussed, and the consequences of sintering Cr and Mn containing steels for the sintering atmosphere are shown. Secondary operations performed in PM parts production are described and typical examples for high performance PM parts are shown, and the dominating trends are identified.

Fiber lasers integration for LMJ

The Fibre-Injection System in the LIL–LMJ facilities makes use of a single-mode fiber based arborescent architecture. Starting from a unique single-mode oscillator, it consists of a high performance PM design which is dedicated to the generation of pulses onto a large number of synchronous outputs. The optical features to be optimised involve dynamic ranges in excess of 50 dB and the generation of 25 ns wide arbitrary waveforms at 100 ps time resolution, of which the PSD looks like a precisely controlled Bessel distribution. We analyse the complete design issues, together with the optical components which have been developed specifically. To cite this article: A. Jolly et al., C. R. Physique 7 (2006).

Sintering and alloy design for high performance PM steels

Strategies to produce high performance steels through enhanced sintering and alloy design received considerable attention in Vienna, with the cost effectiveness of the routes proposed – similar performance at reduced cost or enhanced performance at equivalent cost – being an important part of the considerations.

Fatigued? Swedish experts point the way to high performance PM

Leading steel powder producer Höganäs has built up a unique knowledge bank on fatigue performance after embarking on an unprecedented project to map the microstructure and fatigue performance of its materials in the minutest detail…

Chrome brightens the way for sinter-hardening: Combining sintering and heat-treatment in a single, clean, process step makes sinter-hardening an attractive and cost-effective option for the production of high-performance PM parts…

The economical achievement of premium mechanical properties for PM parts has been pursued over a number of years and a plethora of materials and process studies on sinter-hardening have already been launched. So it was not surprising that the sinter-hardening behaviour of ferrous PM materials was one of the major themes at the Las Vegas conference, writes Joe Capus.

Influence of notches on fatigue of high performance PM materials

Influence of notches on fatigue of high performance PM materials

Synthesis of high performance PM motors with concentrated windings

The windings concentrated around the teeth offer obvious advantages for the electrical machines with radial air-gap, because the volume of copper used in the end-windings can be reduced. The Joule losses are decreased, and the efficiency is improved. These machines are still limited to applications of sub-fractional power and they generally present a reduced number of phases. In the three-phase machines, the concentrated winding is too often restricted to a winding with a short pitch of 120 electrical degrees, i.e., to a winding with performances reduced compared to the traditional structures. But there is a significant number of three-phase structures which can support a concentrated winding if the number of poles is increased. In this article, the authors present a synthesis of the structures of three-phase machines with concentrated windings. (1) In the first part, the structures with a regular distribution of the slots are presented. A systematic method is proposed to determine the windings and the performances are discussed. (2) In the second part, the authors present original structures of three-phase machines with concentrated windings which use an irregular distribution of the slots. A specific method to identify these structures is described, and a comparative analysis of the performances of the original and traditional structures is performed by using a field calculation software.