Powder Metallurgy Materials Research Articles

Effect of Sintering Temperature on the Microstructure and Mechanical and Tribological Properties of Copper Matrix Composite for Brake Pads

Copper-based powder metallurgy materials are frequently utilized in fabricating brake pads for high-speed trains. The preparation process involves mixing, ball milling, pressing, and sintering. Among these steps, hot-pressed sintering stands out as a rapid and efficient method that significantly influences the properties and performance of the products. In this study, four samples (S700/S750/S800/S850) were prepared using hot-pressed sintering at various temperatures, as follows: 700 °C, 750 °C, 800 °C, and 850 °C. The mechanical and physical properties of the four samples were tested, and the microstructure and compositions were investigated using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The findings highlighted the close relationship between sintering temperature and the mechanical and physical properties of the samples, as it impacts the porosity and interfacial bonding of the particles. Notably, Sample S800 demonstrated superior mechanical and thermal conductivity. Furthermore, the coefficient of friction (COF), friction heat, and wear rate of the four samples were also tested under different braking speeds ranging from 150 km/h to 350 km/h. The results indicated that the COFs of the four samples remained relatively stable below 300 km/h but decreased notably above 300 km/h due to heat fading. Sample S800 displayed consistent and high COF under varied braking speeds and exhibited the lowest wear rate. The observed wear mechanisms included abrasive wear and oxidation wear. Additionally, the friction test results underscored the close correspondence of the COF curve of S800 with the standard of the Ministry of Railways of the People’s Republic of China.

Investigation of phase transformation model, densification mechanism, and mechanical properties of TiH2 powder metallurgy materials

TiH2 has gradually gained attention in powder metallurgy because of its unique properties. This study systematically investigated the porosity, density, mechanical tensile properties, and fracture toughness of sintered samples of TiH2 as a powder metallurgy starting material. The results showed that, compared with hydrogenation-dehydrogenation titanium (HDH Ti), the density, elongation, and fracture toughness of the sintered TiH2 samples significantly improved. In addition, the contributions of grain size, porosity, and oxygen content to the yield strength of the samples are discussed, and the results revealed that a lower oxygen content and porosity are the main reasons for the differences in the mechanical properties between HDH Ti and TiH2. Finally, the experimental results are combined with first-principles calculations and simulations to construct a TiH2 phase transition model. The contribution of H atoms to the TiH2 phase transition energy barrier and activation sintering densification was investigated and elucidated, revealing the TiH2 sintering densification mechanism from the perspective of phase transition. The derived results contribute to a deeper understanding of the intrinsic mechanism of TiH2 activation sintering densification, which is highly important for the development of advanced titanium materials.

Three-dimensional super-resolution crack imaging in industrial manufactured components: A truncated correlation photothermal coherence tomography approach

The challenge of detecting cracks in powder metallurgy (PM) components has been a topic of interest for many years, with no practical commercial solution currently in place. This study employs enhanced truncation-correlation photothermal coherence tomography (eTC-PCT) to visualize 3D cracks within PM automotive parts. Through the application of effective diffusion-wave reversal techniques, blurred infrared thermophotonic images of subsurface defects (cracks) in (“green”) compressed metal PM components were restored to their original geometric resolution over the entire depth range. This approach enabled the creation of 3-dimensional depth-resolved photothermal tomographic images and cross-sectional mappings of cracks. The developed technique reveals the precise spatial dimensions of surface and subsurface cracks, reaching depths of down to 3 mm (not an upper limit) that conventional thermal imaging cannot access due to limitations imposed by the depth-integrated nature of conventional thermal-wave imaging, the properties of PM materials, and the physics of spreading diffusion. The super-resolution method was further applied to a sintered automotive part, specifically validating the efficacy of eTC-PCT for non-destructive imaging (NDI) in manufactured automotive components. Diffusion reversal imaging shows promise as a non-destructive testing (NDT) tool, with potential applications in a wide range of manufactured products, including both the green and sintered stages of automotive component production.

Research on self-healing characteristic and state prediction method of the copper based powder metallurgy materials on friction interface

In high power density transmission systems, the friction and wear characteristic of copper based powder metallurgy materials is directly linked to working reliability. Moreover, these materials have frictional self-healing characteristic at the material interface. This paper focuses on exploring the healing mechanism of copper based powder metallurgy materials and conducts ‘damage-healing’ tests, proposing a method to characterize the self-healing characteristic. Subsequently, through comparative tests, the influence of temperature, speed, and pressure on the self-healing characteristics is analyzed. The results show that the increase in temperature reduces the furrow width and depth by 15.30% and 59.76%, respectively. Pressure has the greatest effect on surface roughness, reducing it by 67%. Meanwhile, this paper developed a PSO (Particle Swarm Optimization)-LSTM (Long Short-Term Memory) method to accurately predict the self-healing characterization parameters and self-healing time with small error (average 4.35%) and high correlation coefficient (R 2) (average 0.976). This study contributes to the development of interface repair technology for friction materials.

Friction properties and prediction of a novel copper-based powder metallurgy material modified with TiB2/B4C composite

By incorporating the dual ceramic elements TiB2/B4C, we investigated their impact on the mechanical properties, thermal properties, and friction performance of copper-based powder metallurgy materials, and elucidated the friction wear mechanism. Additionally, machine learning algorithms were employed to predict the friction coefficient and stability coefficient. The conclusions are as follows:With the increase in the TiB2/B4C ratio, the trend of mechanical properties initially increases and then decreases, with the optimum ratio being 5:3 for TiB2 and B4C, exhibiting superior mechanical properties. Moreover, B4C enhances the thermal conductivity of copper-based friction materials more effectively than TiB2. In terms of overall friction performance, the ratio of TiB2 to B4C at 5:3 yields better frictional properties. The primary components of the friction surface friction film are CuO, Cu2O, Fe2O3, and B2O3, transitioning from a ceramic film to a metallic film as the TiB2/B4C ratio increases. The friction wear mechanism shifts from abrasive wear to severe fatigue wear as the TiB2/B4C ratio increases, accompanied by oxidative wear. Furthermore, an AdaBoost algorithm model was developed to effectively predict the friction coefficient and stability coefficient, with accuracies of 0.9993 and 0.8739, respectively.

Experimental investigation of cutting force of powder metallurgy valve guide rod hole

Aiming at the problem of fast wear of machining tools in the special powder metallurgy valve guide rod hole and gasket seat of a certain engine cylinder head, in order to solve the technical problems in the cutting force (CF) of this kind of powder metallurgy materials, different tools are used and the analysis is carried out under different cutting test conditions. The cutting force law and surface roughness change law of similar powder metallurgy materials are determined to determine the appropriate tool materials and processing parameters. The experimental results show that under the same processing conditions, ceramic tools will suffer less than cemented carbide tools and cutting force can obtain a smaller surface roughness. In addition, the mass production process of valve seat, the blade material is ceramic knife.

Effect of Different Content of CeO2 on the Evaluation of Micro-Structure and Wear Data of Boride Layer of Iron Based Powder Metallurgy Materials

Iron base powder metallurgy sample was borided with different content of CeO2 (0 wt.%, 2 wt.%, 4 wt.%) at 950 °C for 5 h by using solid powder boriding method. The wear tests were carried out on the friction and wear tester model MPX-3G. Scanning electron microscope (SEM), X-ray diffraction analysis, Rockwell hardness tester model Huayin HR-150A and three-dimensional non-contact tester model ST400 were used in the evaluation of micro-structure and wear data. The results show that samples with best performance in the evaluation of micro-structure and wear tests were borided with 2% CeO2.

Vplyv technológie tepelného spracovania na tribologické vlastnosti vybraných oceľových materiálov

The heat treatment technology changes all sorts of materials properties. We examined the change of tribological properties of selected powder metallurgy materials and conventional steels, in this article. We used special testing equipment, for measuring the changes of friction coefficient of individual tested materials, before application of the heat treatment and after application of the heat treatment. We tested two types of powder metallurgy steels and two types of conventional steels. The changes in friction coefficient are shown in the table and charts. We used boronising, nitriding and surface hardening as procedures of heat treatment.

Retracted: Automatic Measurement of Nanoimage Based on Machine Vision and Powder Metallurgy Materials

Retracted: Automatic Measurement of Nanoimage Based on Machine Vision and Powder Metallurgy Materials

Retracted: Construction and Performance Research of Reinforced Iron-Based Powder Metallurgy Materials Based on Phyllanthin as Drug Transport Carriers

Retracted: Construction and Performance Research of Reinforced Iron-Based Powder Metallurgy Materials Based on Phyllanthin as Drug Transport Carriers

Effect of hot rolling on microstructure and mechanical properties of hot isostatically pressed 30CrMnSiNi2A ultrahigh strength steel

The prior particle boundaries (PPBs) are a typical powder metallurgy (PM) defect, which usually leads to the deterioration of mechanical properties in PM materials. In this study, two different hot rolling modes (unidirectional rolling and cross rolling) are designed to improve PPBs in hot isostatic pressed (HIPed) 30CrMnSiNi2A ultrahigh strength steel. The microstructure, mechanical properties and fracture features of the HIPed compact, the hot unidirectional rolled (HURed) and hot cross rolled (HCRed) sheets are systematically compared. The results manifests that hot rolling has a significant influence on size and distribution of PPBs. PPBs in HIPed compact are comprised of Al-rich oxides which is distributed along particle boundaries. After hot rolling, large PPBs inclusions are crushed and the size of PPBs are mostly concentrated in 0–0.20 μm. Unidirectional rolling makes continuous PPBs structure broken into short-chain fragments and dispersed oxides completely, while cross rolling makes most of continuous PPBs structure maintained and only a few oxides are dispersed. Excellent mechanical properties are obtained by hot rolling, reflecting on an ultimate tensile strength (UTS) of about 2.0 GPa, a total elongation (TE) of 17.9 %, a Charpy impact energy of 28.6J along rolling direction and a UTS of over 2.1 GPa, a TE of 16.1 %, a Charpy impact energy of 18.1J along transverse direction, respectively. High performances can be attributed to formation of martensite, grain refinement, improvement of PPBs and work hardening. Furthermore, hot-rolled samples manifests an obvious anisotropy in mechanical properties. The HCRed sample reveals a lower anisotropy compared to the HURed sample, mainly owing to differences of PPBs distribution and rolling textures.

The rapid densification behavior of powder metallurgy Ti alloys by induction heating sintering

Micropores are decisive to mechanical properties and thermal deformation capabilities of powder metallurgy (P/M) Ti alloys sintered compacts. As a result, achieving express densification is of prime importance and has attracted increasing attention recently. Induction heating owns the merits of high efficiency, short process, and low cost, and thus has huge potential to be used as a sintering approach for the fabrication of P/M Ti alloys. Nevertheless, the facilitated densification behavior associated with induction heating sintering remains unclear so far. To address it, powder metallurgy Ti6Al4V is manufactured via induction heating sintering with which the underlying sintering mechanism is investigated in-depth. It is found that induction heating could generate a fully densified compact in a remarkably shortened time, demonstrating its superior sintering efficiency as compared with conventional resistance furnace heating. COMSOL finite element analysis reveals that the maximum current density during induction heating can reach 106 A m–2 though the magnetic field strength is solely 0.02 T, leading to a slight temperature difference of approximately 30 °C between the interior and exterior of the billet. Furthermore, the rapid heating essentially starts at sharp corners of particles due to the potent current concentration effect, which facilitates the cracking of the particle surface oxide film and thus enhances the direct contact between them. Moreover, the electromigration effect caused by induction current promotes the diffusion capability of elements, giving rise to expedited densification, alloying, and chemical homogenization. This work provides not only critical insight into the sintering mechanism of induction heating sintering but also significant guidance for low-cost powder metallurgy materials preparation.

Effect of Iron Powder Type on Friction and Wear Properties of Copper-Based Friction Powder Metallurgy Material

The sintered copper-based friction materials for high-speed train brake pads have a complex composition that should possess good physical, mechanical, and tribological properties in practical applications. For this article, four kinds of friction materials were prepared by powder metallurgy technology and the effects of iron powders on the microstructural and tribological properties of copper-based friction materials were characterized using a scanning electron microscope (SEM) and x-ray diffraction (XRD). The results showed that iron powder as an enhancing component could effectively change the friction and wear properties of the experimental materials. The copper-based friction materials containing hydroxy iron (1–5 μm) have a relatively higher coefficient of friction: The friction coefficient was significantly improved by 16.8% compared with reduced iron under a rotation speed of 4000 r/min. The friction coefficient of friction material containing water-atomized iron powder is relatively reliable with 3000–7000 r/min speed range. In a high-speed environment, the friction surface of material containing reduced iron or hydroxy iron (1–5 μm) mainly has cracks and brittle fractures, and the material containing hydroxy iron (10 μm) or water-atomized iron has an obvious layered structure and shows fatigue wear.

Research on hot isostatic pressing sintering behavior of 90W–Ni–Fe–Cu alloy

In order to understand the underlying material evolution during liquid phase sintering (LPS) process in hot isostatic pressing process (HIP), microstructure and mechanical properties of 90 W–Ni–Fe–Cu alloys fabricated at 1400 °C/150 MPa are examined systematically. For 90W-4.2Ni-1.8Fe–4Cu alloy, the typical LPS microstructure, which are spherical W grains uniformly surrounded by continuously distributed γ- (Ni, Fe, Cu) matrix phase with the lowest W–W contiguity of 0.31, is achieved successfully after HIP at 1400 °C/150 MPa. The excellent tensile strength reaches as high as 873 MPa with elongation of 17.3% due to the soft γ- (Ni, Fe, Cu) matrix phase. Moreover, the relationship between the microstructure parameters VM(1−CW−W) and elongation ε are established and analyze the association with dislocation motion in depth through electron backscattered diffraction (EBSD) characterization. To our best knowledge, the LPS behavior of tungsten alloy is in-situ revealed by high-temperature confocal scanning laser microscopy (HT-CSLM) for the first time. The current research provides a novel strategy for designing and fabricating powder metallurgy materials by LPS with pressure.

Modeling of the Sintered Density in Cu-Al Alloy Using Machine Learning Approaches.

In powder metallurgy materials, sintered density in Cu-Al alloy plays a critical role in detecting mechanical properties. Experimental measurement of this property is costly and time-consuming. In this study, adaptive boosting decision tree, support vector regression, k-nearest neighbors, extreme gradient boosting, and four multilayer perceptron (MLP) models tuned by resilient backpropagation, Levenberg-Marquardt (LM), scaled conjugate gradient, and Bayesian regularization were employed for predicting powder densification through sintering. Yield strength, Young's modulus, volume variation caused by the phase transformation, hardness, liquid volume, liquidus temperature, the solubility ratio among the liquid phase and the solid phase, sintered temperature, solidus temperature, sintered atmosphere, holding time, compaction pressure, particle size, and specific shape factor were regarded as the input parameters of the suggested models. The cross plot, error distribution curve, and cumulative frequency diagram as graphical tools and average percent relative error (APRE), average absolute percent relative error (AAPRE), root mean square error (RMSE), standard deviation (SD), and coefficient of correlation (R) as the statistical evaluations were utilized to estimate the models' accuracy. All of the developed models were compared with preexisting approaches, and the results exhibited that the developed models in the present work are more precise and valid than the existing ones. The designed MLP-LM model was found to be the most precise approach with AAPRE = 1.292%, APRE = -0.032%, SD = 0.020, RMSE = 0.016, and R = 0.989. Lately, outlier detection was applied performing the leverage technique to detect the suspected data points. The outlier detection discovered that few points are located out of the applicability domain of the proposed MLP-LM model.

Manufacturing and Properties of Spherical Iron Particles from a By-Product of the Steel Industry

In modern cold rolling mills in the steel industry, iron oxide powder is produced as a by-product when used pickling agents are recycled. Further processing of these iron oxide powders could enable the production of iron powder for various applications in powder metallurgy. For this purpose, a new process route with an eco-friendly hydrogen reduction treatment was developed. The process is able to manufacture a variety of iron particles through minor process adaptations. It was possible to manufacture spherical iron particles with high flowability. The flowability was measured by a Revolution Powder Analyzer, and an avalanche angle of 47.7° of the iron particles was determined. In addition, the bulk density measurements of the processed iron particles collective achieved values of 3.58 g/cm3, and a spherical morphology could be observed by SEM analysis. The achieved properties of the iron particles show high potential for applications where high flowability is required, e.g additive manufacturing, thermal spray and hot isostatic pressing. By adjusting the process conditions of the developed process, irregular iron particles could also be manufactured from the same iron oxide powder with a very high specific surface of 1640 cm2/g and a low bulk density of 1.23 g/cm3. Therefore, the property profile is suitable as a friction powder metallurgy material. In summary, the developed process in combination with the iron oxide powder from steel production offers a cost-efficient and sustainable alternative to conventional iron powders for additive manufacturing and friction applications.

Forging of PM Ti–6Al–4V alloy at the temperature above β-transus and high strain rate: modeling and trials in industrial conditions

The results of the forging process in open dies of the powder metallurgy (PM) Ti–6Al–4V alloy, carried out at the temperature above β-transus and at a high strain rate were presented. As an initial material for the research relatively cheap elemental powders were used. This approach gives a real chance for the implementation of the developed technologies. As the range of phase transition temperature in titanium alloys is influenced also by the technology of their production, the β-transus temperature was estimated for the PM Ti–6Al–4V alloy. Finite element method (FEM) numerical analysis of the forging process at the temperature of 1000 °C and high strain rate was performed. The results obtained by the FEM modeling were verified under industrial conditions. The forging trials were made at the temperature of 1000 °C on a screw press operating at a speed of 250 mm s−1. For comparison, the alloy was also studied in as-cast and hot-rolled conditions, which is widely used as a feedstock. The influence of the method of manufacturing feedstock on the microstructure and selected properties of the forgings was determined. This approach allowed for a qualitative assessment of the PM material. The forging process in open dies of two different feedstocks led to the production of forgings with a uniform and similar lamellar microstructure. Thus, it was shown that the heating conditions, the parameters of the forging process, and the method of cooling the product after forging have a decisive influence on the microstructure condition of the forgings shaped in the temperature range of the β phase.

New powder metallurgy preparation method of homogeneous and isomeric Al−Cu−Mg mixed crystal materials

A new idea of homogeneity isomerism is proposed in this work to break through the single restriction that traditional homogeneous powder metallurgy materials take refining particles as the only modification method. AA2024 alloy powders of different diameters are mixed in a certain proportion through low-energy ball milling, and then a kind of mixed crystal material is successfully fabricated by hot pressing sintering. The results show that the grain morphology of the traditional sample sintered with single-diameter particles tends to become irregular polygon shape, while the grain morphology of the mixed crystal materials forms a special structure in which larger grains are coated with smaller grains. Compared with the former, when the proportion of coarse particles is 20% (mass fraction), the tensile strength increases by 38.8%; when the proportion of coarse particles is 50%, the elongation increases by 14%. The mixed crystal material exhibits a mixed fracture mechanism of intergranular fracture and transgranular fracture, and the pinning effect of the second phase on the dislocation is more obvious, so the properties of the alloy are improved significantly. The above research provides a new idea for the preparation of high-performance homogeneous isomeric mixed crystal materials.

Experimental Study on Friction Interface Self-healing Performance of Copper-based Powder Metallurgy Materials

Experimental Study on Friction Interface Self-healing Performance of Copper-based Powder Metallurgy Materials

The Investigation on Dimensional Stability in Some Sintered Powder Metallurgy Alloys

The subject of this research was to study the effect of sintering time on the dimensional characteristics of some powder metallurgy (PM) materials. The powders used in this study are prealloyed iron-based powders with Cu, Ni and Mo. The powders were single pressed at 600 MPa and the disc specimens have the dimensions of 8-6 mm. The green compacts were sintering in a laboratory furnace at 1150 ºC for 60, 75 and 90 minutes and air-cooled to room temperature. The density of green and sintered specimens, the porosity and the dimensional changes were evaluated.