# Applications of Tungsten Pseudo-Alloys in the Energy Sector
## 3 Conclusions  
In general, \"heavy\" flywheels are conceptually simpler and, therefore, more reliable, while high-speed \"light\" flywheels usually have higher specific storage capacities, tend to be more expensive and generally less reliable. This is determined by the amount of kinetic energy deposited, which is also a limiting factor for the material properties. Increasing the density of the material used places increased demands on the material strength under otherwise equal conditions, thus limiting the maximum allowable rotor speed. For this experiment, three W-MMC materials, made from powders obtained through oxidation-reduction recycling of machining waste chips, were prepared with strength characteristics suitable for the expected use. However, only two of them have sufficient properties to be considered full replacements for steel flywheels. These materials are TNRC with strength \(\mathrm{R_{m}}=\mathrm{R_{p0.2}}>1600\) MPa and TRC with \(\mathrm{R_{m}}=\mathrm{R_{p0.2}}>1250\) MPa. The substitution of steel with other metallic construction materials only makes sense if it leads to an increase in the storage capacity of the flywheel under the same conditions. A low-alloy steel flywheel in the shape of a disc made from a commercially available material with the specification DIN/EN 2 CrMo4 (AISI 4142) was chosen as a basis for comparison. This steel is characterised by its toughness, good torsional strength, and good fatigue strength. It is typically used for statically and dynamically stressed vehicle components, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **R\({}_{\text{p0.2}}\)** & **R\({}_{\text{m}}\)** & **A\({}_{\text{5}}\) (\%) after** & \\  & **(MPa)** & **(MPa)** & **Quenching** & **Density (g/cm\({}^{3}\))** \\ \hline TNRC & & & & \\ quenching & 651/660/671 & 1023 & 21.1/26.6/28.0 & 17.48–17.49 \\ Forging, ageing & & 1600/1610/1619 & 5.7/7.6/8.2 & \\ \hline DSRC & & & & \\ quenching & 652/660/671 & 948/956/967 & 17.4/18.7/19.1 & 18.25–18.30 \\ Forging, ageing & & & & \\ \hline TRC & & & & \\ quenching & 658/665/67 & 948/965/1001 & 17.1/18.1/19.3 & 18.26–18.29 \\ Forging, ageing & & 1281/1484/1501 & 1.1/2.6/4.9 & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Overview of the mechanical properties achieved by materials made from recycled powders. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **TN** & **TNRC 0.15** & **TNRC 0.09** \\ \hline \multirow{4}{*}{Chemical composition (wt.\%)} & W & 91.00 & 91.35 & 91.38 \\  & Ni & 6.00 & 5.70 & 5.75 \\  & Co & 3.00 & 2.80 & 2.78 \\  & Fe & 0.00 & 0.15 & 0.09 \\ \hline \multirow{4}{*}{Mechanical properties *} & R\({}_{\text{p0.2}}\) (MPa) & 648;659;649;652;658 & 649;649;652;653 & 656 \\  & R\({}_{\text{m}}\) (MPa) & 1023;1026;1020;1023;1022 & 1018;1016;1018;1015 & 1017 \\  & A\({}_{\text{5}}\) (\%) & 39.5/37;1,357;36,837.0 & 36.1,333;6,36,03.27 & 28.0 \\  & Impact test (J/cm\({}^{2}\)) & 248\(>\)300;170 \(>\) 300;300 & 277,164;\(>\)300;184 & 186 \\ \hline \multirow{4}{*}{Mechanical properties **} & R\({}_{\text{m}}\) (MPa) & 1605;1622;1610; & 1603;1600;1602;1608;1602;1619; & \\  & 1604;1608;1622;1615 & 1616 & 1601;1499;1589 \\ \cline{1-1}  & A\({}_{\text{5}}\) (\%) & 7.39;57.2;9,69.8/3.9 & 6.8/8.2;7.6/8.0.6;5.7/1.5;7 & 0.4;0.0;0.2 \\ \hline \hline \end{tabular}
* * material was sintered and quenched only. ** after swaging (reduction of 36%) and ageing (423 *C/2 h).  
\end{table} 
Table 7: Effect of the chemical composition of TNRC on mechanical properties. engines and machinery, as well as for larger cross-section parts, crankshafts, and gears. The yield strength of this steel depends on the dimensions of the semi-finished product, with larger diameters reaching 500 MPa [18]. In this case, the substitution of the flywheel material by replacing a conventional structural steel with yield strength R\({}_{\text{p0.2}}\) = 500 MPa with TNRC material with R\({}_{\text{p0.2}}\) > 1600 MPa will increase the amount of stored energy per unit mass by 36%.