Effect of Alloying Type and Lean Sintering Atmosphere on the Performance of PM Components

In order to be cost effective and to meet increasing performance demands, powder metallurgy steel components require continuous improvement in terms of materials and process development. This study demonstrates the feasibility of manufacturing structural components using two different alloys systems, i.e. lean Cr-prealloyed and diffusion bonded water atomised powders with different processing conditions. The components were sintered at two different temperatures, i.e. 1120 and 1250 \ub0C for 30 minutes in three different atmospheres: vacuum, N2-10%H2 atmosphere as well as lean N2-5%H2-0.5%CO-(0.1-0.4)%CH4 sintering atmosphere. Components after sintering were further processed by either low pressure carburizing, sinterhardening or case hardening. All trails were performed in the industrial furnaces to simulate the actual production of the components. Microstructure, fractography, apparent and micro hardness analyses were performed close to the surface and in the middle of the sample to characterize the degree of sintering (temperature and atmosphere) and the effect of heat treatment. In all cases, components possess mostly martensitic microstructure with a few bainitic regions. The fracture surface shows well developed sinter necks. Inter- and trans-granular ductile and cleavage fracture modes are dominant and their fraction is determined by alloy and processing rout

Manufacturing of Valve Bridge Component Utilizing Lean Alloyed Powders and Vacuum Sintering

Increasing the application area of powder metallurgy (PM) steels for\ua0manufacturing of high-performance structural components results in\ua0material saving, reduction in energy consumption, etc. In this study,\ua0feasibility of the manufacturing of valve bridge component for heavy duty\ua0engine utilizing lean alloyed powders and novel vacuum sintering\ua0approach, followed by low pressure carburizing, is studied. Three low\ua0alloyed steel powders were processed by conventional uniaxial pressing\ua0and sintering at 1120 and 1250\ub0C in industrial vacuum furnace. The\ua0components were tested under high cycle fatigue testing, simulating real\ua0conditions of operation. Fatigue properties did not show significant\ua0dependence on the sintering temperature and were comparable to\ua0currently used reference cast material. Fracture surfaces of broken\ua0samples were analyzed to detect crack initiations and fracture\ua0mechanisms as well as quality of sintering. Results showed preferentially\ua0ductile failure, well developed sintering necks and clean pore surfaces,\ua0indicating good sintering. Tested material in combination with novel\ua0vacuum sintering process show to be an attractive alternative for\ua0manufacturing of this type of components for heavy duty engineapplications

Surface chemistry of the titanium powder studied by XPS using internal standard reference

Surface chemistry of the titanium powder has particularly growing interest due to the increasing application of titanium components prepared by powder metallurgy, in particular metal injection moulding and additive manufacturing. Due to the high chemical activity, number of titanium oxides, calcium and complex Ca–Ti–oxides can be expected on the component/medical implant surface, depending on powder and component manufacturing and post-treatment, but are very difficult to analyse due to the lack of the experimental data and analysis methodology. Therefore, a methodology for the analysis of the surface chemistry of the Ti-powder by XPS utilising internal standard reference was developed. The obtained methodology was used for the surface analysis of titanium powder and identification of its surface oxide composition. The results show that the powder surface is covered by TiO2 layer in the form of rutile with a thickness of 4.4 nm. Carbon and nitrogen impurities were also found present on the powder surface

Characterization Of The Virgin And Re-cycled Nickel Alloy HX Powder Used For Selective Laser Melting

Taking to account high specific surface area of the powder, its surface state becomes one of the most important aspects of usability of the powder in PM process and particularly in additive manufacturing. Powder surface characterization of the two HX Ni-based superalloy powders sampled during selective laser melting – namely virgin and re-cycled powders was performed by means of XPS and high-resolution SEM combined with EDX. Results showed slight difference in surface chemical composition between the powders. The most sensitive to oxidation alloying elements in the powder – Al and Cr – segregate to the surface to form more stable oxides in case of re-cycled powder. Loss of silicon due to sublimation was also detected on the surface of re-cycled powder. Ni, as a base element, was presented in the form of hydroxide on the as-received surface of both investigated powders

Characterization of the virgin and recycled nickel alloy hx powder used for selective laser melting

Taking to account high specific surface area of the powder, its surface state becomes one of the most important aspects of usability of the powder in PM process and particularly in additive manufacturing. Powder surface characterization of the two HX Ni-based superalloy powders sampled during selective laser melting-namely virgin and re-cycled powders was performed by means of XPS and high-resolution SEM combined with EDX. Results showed slight difference in surface chemical composition between the powders. The most sensitive to oxidation alloying elements in the powder-Al and Cr-segregate to the surface to form more stable oxides in case of re-cycled powder. Loss of silicon due to sublimation was also detected on the surface of re-cycled powder. Ni, as a base element, was presented in the form of hydroxide on the as-received surface of both investigated powders

Surface Characterization Of 60Cu-40Sn Bronze Powder

Due to the high surface area of the powder, reactivity of the material is significantly enhanced meaning that the presence of the surface oxide layer in unavoidable. The determination of the surface oxide layer composition is necessary to facilitate surface oxide removal during sintering by the adjustment of the sintering conditions. The surface chemical analysis of the 60Cu40Sn bronze powder was performed by means of X-ray photoelectron spectroscopy (XPS) and high-resolution scanning electron microscopy combined with energy dispersive X-ray analysis (HR SEM+EDX). Determination of the surface oxide layer thickness and compositional profiles was done by altering of ion etching and XPS analysis. The results showed tin oxide enrichment at the surface of the powder particles. The traces of impurities like Ca, P and Zn were also detected on the top surface of the powder

Surface Characterization Of 60Cu-40Sn Bronze Powder

Due to the high surface area of the powder, reactivity of the material is significantly enhanced meaning that the presence of the surface oxide layer in unavoidable. The determination of the surface oxide layer composition is necessary to facilitate surface oxide removal during sintering by the adjustment of the sintering conditions. The surface chemical analysis of the 60Cu40Sn bronze powder was performed by means of X-ray photoelectron spectroscopy (XPS) and high-resolution scanning electron microscopy combined with energy dispersive X-ray analysis (HR SEM+EDX). Determination of the surface oxide layer thickness and compositional profiles was done by altering of ion etching and XPS analysis. The results showed tin oxide enrichment at the surface of the powder particles. The traces of impurities like Ca, P and Zn were also detected on the top surface of the powder

Copper Bronze Powder Surface Studied by XPS and HR SEM

The state of the powder surface represents one of the main interests in the whole cycle of components’ production using powder metallurgy (PM) route. Large specific surface area of the powder in combination with often alloying with oxygen sensitive elements results in oxidation of the powder surface in most of the cases. The information about surface chemistry of the powder is of vital importance for further consolidation and sintering steps. Surface sensitive analytical techniques – X-ray photoelectron spectroscopy (XPS) and high-resolution scanning electron microscopy combined with energy dispersive X-ray analysis (HR SEM+EDX) were used for surface chemical analysis of the 60Cu-40Sn bronze powder. Determination of the compositional profiles and estimation of the surface oxide layer thickness was done by altering of ion etching and XPS analysis. The results showed tin oxide enrichment and presence of copper hydroxide on the surface of the powder particles. The impurities of P, Zn and Ca were also detected on the top surface of the powder in trace amounts

Influence Of Cr Alloying Content On The Surface Oxide Composition In Case Of Water-atomized Steel Powder

Utilization of chromium as an alloying element for water atomized steel powder improves cost and performance efficiency for PM steels. However, presence of Cr puts strict demands on the component manufacturing process due to high oxygen sensitivity of chromium. Hence its effect on surface oxide distribution is of vital importance for the tailoring of the sintering process. A number of experimental steel powders, alloyed with 0 to 4 wt.% of chromium, were prepared by water atomization with subsequent annealing in lab-scale equipment. Powder manufacturing process conditions were kept the same for all the powders. The effect of chromium content in the powder on the surface oxide layer thickness and distribution of particulate oxides features on the powder surface was studied by XPS and HRSEM+EDX

Surface oxide state on metal powder and its changes during additive manufacturing: An overview

Quality and usefulness of the powder for additive manufacturing (AM) are strongly determined by the surface composition of the powder. In addition, taking into account harsh conditions during AM process, significant changes in the powder surface chemical composition are taking place, limiting powder recyclability. Hence, knowledge concerning amount of oxides, their composition and spatial distribution on the powder surface determines further powder recycling. This communication summarizes possibilities of qualitative and quantitative analysis of powder surface chemistry by surface-sensitive chemical analyses using XPS and HR SEM coupled with EDX. The effect of alloy composition, AM process applied and powder handling on the surface composition of the powder are addressed. Results indicate significant enrichment in the thermodynamically stable surface oxides in case of high-alloyed powder for both, EBM and LS processes. A generic model for the oxide distribution, depending on the alloy composition and powder surface degradation during AM manufacturing, is proposed