Microstructure Development in Powder Metallurgy Steels: Effect of Alloying Elements and Process Variables

2014 ◽  
Vol 782 ◽  
pp. 467-472 ◽  
Author(s):  
Eduard Hryha ◽  
Lars Nyborg
Keyword(s):  
Powder Metallurgy ◽  
Carbon Sources ◽  
Processing Parameters ◽  
Alloying Elements ◽  
Microstructure Formation ◽  
Prealloyed Powder ◽  
Conventional Sintering ◽  
The Difference ◽  
Characteristic Features ◽  
Effect Of Alloying

Microstructure of the powder metallurgy (PM) steels and especially mechanism of its formation differs significantly from the microstructure of the conventional steels even if composition will be exactly the same. The difference is not only connected to the presence of the pores, which are inalienable feature of the PM parts. Presence of the prior inter-particle boundaries, which can be contaminated by residual oxides, as well as microstructure heterogeneity are another characteristic features of the microstructure of PM steels. Microstructure heterogeneity is connected to the PM manufacturing process: powder mix, consisting of the base powder and additional alloying elements is compacted and then sintered. Fully prealloyed powder is not always possible to use in standard press & sintering route due to the solid solution strengthening of the ferrite resulting in bad powder compressibility. Hence, in order to provide good powder compressibility only pure iron or low-alloyed (typically <3 wt.%) powders are used. Required alloying elements and carbon (added as graphite) are further admixed in the powder form and are distributed during sintering by diffusion into iron particles at high temperatures. To assure satisfactory distribution of alloying elements, oxide layer, covering surface of the powder particles and hindering mass-transfer of the alloying elements, has to be removed first. This can be done by gaseous reducing agents as hydrogen and carbon monoxide. However, their cost and/or purity are of issue for modern alloyed PM steels. Admixed carbon, additionally to its function as alloying element, plays a role of effective reducing agent at higher temperatures. Paper summarizes the main features of microstructure formation during the whole sintering cycle (heating and isothermal sintering) and effect of alloying additives (different carbon sources, alloying elements) and processing parameters (sintering atmosphere composition, temperature profile) on the microstructure formation during conventional sintering process. Results indicate that for successful sintering of alloyed PM steels with homogeneous defect-free microstructure, hydrogen-rich atmospheres and high-temperature sintering are required.

scholarly journals Influence of alloying components on diffusion and bonding processes in powder materials

2021 ◽  
Vol 2131 (4) ◽  
pp. 042024
Author(s):  
M Egorov ◽  
R Egorova ◽  
A Atrohov ◽  
V Ekilik
Keyword(s):  
Powder Metallurgy ◽  
Rapid Development ◽  
Alloying Elements ◽  
Powder Materials ◽  
Iron Powders ◽  
Cast Steels ◽  
Wide Range ◽  
Aerospace Technology ◽  
Alloy Steels ◽  
Characteristic Features

Abstract At present, powder materials are used in practically all branches of industry, from medicine to aerospace technology. This is a wide range of materials ranging from constructional and instrumental materials and ending with special-purpose materials and medical implants. Powder metallurgy methods are most often used where the manufacture of products with desired properties is impossible using traditional methods: casting, stamping, etc. The production of all these materials is based on such basic operations as: obtaining starting materials, molding from these materials blanks of a given shape, size and strength, and sintering, intended for the final formation of the required properties and dimensions. The peculiarity of powder metallurgy technology allows creating a huge variety of developed technological schemes, which puts these technologies to a new level and allows for the rapid development of many industries. Alloying powder steels, in contrast to cast steels, has a number of characteristic features due to the specificity of their production. The structure of powder alloy steels and their properties depend on the methods of obtaining steels and technological features of their production. The following main methods of obtaining powder alloyed steels can be named: preparation of multicomponent mixtures of powders of iron and alloying elements and their subsequent processing; the use of alloyed iron powders, to which, if necessary, add carbon or other alloying elements; impregnation with liquid alloying metals or diffusion saturation of frameworks sintered from iron powders.

scholarly journals The effect of alloying elements on the properties of pressed and non-pressed biodegradable Fe–Mn–Ag powder metallurgy alloys

Heliyon ◽  
2019 ◽  
Vol 5 (9) ◽  
pp. e02522 ◽  
Author(s):  
Malcolm Caligari Conti ◽  
Bertram Mallia ◽  
Emmanuel Sinagra ◽  
Pierre Schembri Wismayer ◽  
Joseph Buhagiar ◽  
...  
Keyword(s):  
Powder Metallurgy ◽  
Alloying Elements ◽  
Effect Of Alloying

Effect of alloying elements on the properties of Ti-Al-Si alloys prepared by powder metallurgy

2021 ◽  
Vol 868 ◽  
pp. 159251
Author(s):  
Anna Knaislová ◽  
Vendula Šimůnková ◽  
Pavel Novák ◽  
Filip Průša ◽  
Marcello Cabibbo ◽  
...  
Keyword(s):  
Powder Metallurgy ◽  
Alloying Elements ◽  
Effect Of Alloying

Effect of Alloying Elements on the Tooling Capabilities of High Speed Steels Fabricated by Powder Metallurgy

2013 ◽  
Vol 55 (1) ◽  
pp. 43-46
Author(s):  
Guven Orkun Toptop ◽  
Alptekin Kisasoz ◽  
Ahmet Karaaslan
Keyword(s):  
Powder Metallurgy ◽  
High Speed ◽  
Alloying Elements ◽  
Effect Of Alloying

scholarly journals Large-Scale Analysis of the Spatiotemporal Changes of Net Ecosystem Production in Hindu Kush Himalayan Region

2021 ◽  
Vol 13 (6) ◽  
pp. 1180
Author(s):  
Da Guo ◽  
Xiaoning Song ◽  
Ronghai Hu ◽  
Xinming Zhu ◽  
Yazhen Jiang ◽  
...  
Keyword(s):  
Large Scale ◽  
Net Primary Production ◽  
Carbon Sink ◽  
Carbon Sources ◽  
Spatial Dynamics ◽  
Tibet Plateau ◽  
Geostatistical Model ◽  
Hindu Kush ◽  
Temporal And Spatial ◽  
The Difference

The Hindu Kush Himalayan (HKH) region is one of the most ecologically vulnerable regions in the world. Several studies have been conducted on the dynamic changes of grassland in the HKH region, but few have considered grassland net ecosystem productivity (NEP). In this study, we quantitatively analyzed the temporal and spatial changes of NEP magnitude and the influence of climate factors on the HKH region from 2001 to 2018. The NEP magnitude was obtained by calculating the difference between the net primary production (NPP) estimated by the Carnegie–Ames Stanford Approach (CASA) model and the heterotrophic respiration (Rh) estimated by the geostatistical model. The results showed that the grassland ecosystem in the HKH region exhibited weak net carbon uptake with NEP values of 42.03 gC∙m−2∙yr−1, and the total net carbon sequestration was 0.077 Pg C. The distribution of NEP gradually increased from west to east, and in the Qinghai–Tibet Plateau, it gradually increased from northwest to southeast. The grassland carbon sources and sinks differed at different altitudes. The grassland was a carbon sink at 3000–5000 m, while grasslands below 3000 m and above 5000 m were carbon sources. Grassland NEP exhibited the strongest correlation with precipitation, and it had a lagging effect on precipitation. The correlation between NEP and the precipitation of the previous year was stronger than that of the current year. NEP was negatively correlated with temperature but not with solar radiation. The study of the temporal and spatial dynamics of NEP in the HKH region can provide a theoretical basis to help herders balance grazing and forage.

scholarly journals Numerical Simulation of Effect of Different Initial Morphologies on Melt Hydrodynamics in Laser Polishing of Ti6Al4V

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 581
Author(s):  
Kai Li ◽  
Zhenyu Zhao ◽  
Houming Zhou ◽  
Hao Zhou ◽  
Jie Yin ◽  
...  
Keyword(s):  
Flow Behavior ◽  
Processing Parameters ◽  
Surface Finishing ◽  
Polished Surface ◽  
Laser Polishing ◽  
Starting Position ◽  
Double Spiral ◽  
The Difference ◽  
Thermocapillary Forces ◽  
Surface Morphologies

As a surface finishing technique for rapid remelting and re-solidification, laser polishing can effectively eliminate the asperities so as to approach the feature size. Nevertheless, the polished surface quality is significantly sensitive to the processing parameters, especially with respect to melt hydrodynamics. In this paper, a transient two-dimensional model was developed to demonstrate the molten flow behavior for different surface morphologies of the Ti6Al4V alloy. It is illustrated that the complex evolution of the melt hydrodynamics involving heat conduction, thermal convection, thermal radiation, melting and solidification during laser polishing. Results show that the uniformity of the distribution of surface peaks and valleys can improve the molten flow stability and obtain better smoothing effect. The high cooling rate of the molten pool resulting in a shortening of the molten lifetime, which prevents the peaks from being removed by capillary and thermocapillary forces. It is revealed that the mechanism of secondary roughness formation on polished surface. Moreover, the double spiral nest Marangoni convection extrudes the molten to the outsides. It results in the formation of expansion and depression, corresponding to nearby the starting position and at the edges of the polished surface. It is further found that the difference between the simulation and experimental depression depths is only about 2 μm. Correspondingly, the errors are approximately 8.3%, 14.3% and 13.3%, corresponding to Models 1, 2 and 3, respectively. The aforementioned results illustrated that the predicted surface profiles agree reasonably well with the experimentally measured surface height data.

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