OUTSTANDING WEAR Resistance ON TITANIUM GRADE 5 ACHIEVED BY EXPANITEHARD-TI surface hardening TREATMENT
Titanium Grade 5 Wear Test G133
Wear is a common cause of failure of machine components causing costly repairs and downtimes. Wear resistance of Titanium alloys, such as Grade 5 (Ti6Al4V), although better than the relatively softer untreated austenitic stainless steels such as AISI 316L (1.4404) is still not comparable with that of harder materials.
With ExpaniteHard-Ti® surface hardening treatment the specific wear rate, as tested via ASTM g133 Standard Test Method for Linearly Reciprocating Ball-on Flat Sliding Wear, was measured to be reduced over 370 times. This process can be applied to significantly improve the lifetime of costly Titanium parts!
Ball-on-flat sliding wear test (ASTM G133)
The standardised ASTM G133 test geometry consists of a pin with a ball shaped tip made of 100Cr6 alloy with hardness over 800HV. The ball tip is then slid across the test sample with a reciprocating motion and a contact force of 5N. A fixed number of strokes with an amplitude of 10mm at a frequency of 5Hz is made to achieve a total travel distance of 50m.
After the completion of the test, the wear track is measured with a profilometer. From this data, values for the depth and volume of the wear track can be gathered, and specific wear rate can be calculated.
Advanced process for advanced alloys
Advanced engineering materials such as Titanium and its alloys require tailored solutions to improve their properties. The ExpaniteHard-Ti process family was developed for applications where pervasive wear is a problem, and cracking of hard coatings is not acceptable. The treatment process is a single-step solution providing a layer of expanded alpha phase (α-Ti), stabilised by dissolution of oxygen atoms into the crystal structure, forming a conversion layer.
The resulting alpha-case has a hardness of around 900HV – almost three times that of untreated Ti6Al4V. The hardened case depth can vary from 10μm up to 30μm. The microstructure of a 30µm process version can be seen in Figure 1. The hardness profile measured with Vickers Hardness Tester and a 10g load (HV0.01) over 200µm depth is shown in Figure 2.
Figure 1.: Microphotograph of ExpaniteHard-Ti30 on alloy Ti6Al4V (Titanium Grade 5) (x40 magnification).
Figure 2.: Hardness profile of ExpaniteHard-Ti30 on alloy Ti6Al4V (Titanium Grade 5) (fitted power curve to guide the eye).
Figure 3.: Wear tracks’ profiles showing benefits of applying ExpaniteHard-Ti®30 (smoothing: Gaussian filter, cut off 0.08mm).
Over 370 times improvement in wear rate
The profiles of wear tracks measured after the test on both ExpaniteHard-Ti30 treated and untreated Titanium Grade 5 alloy (Ti6Al4V) are shown in the graph in Figure 3. The profiles were used to calculate wear scar volumes. The specific wear rates calculated for both surface finishes were 0.001 mm3/N.m and 0.0000027 mm3/N.m for untreated and treated samples respectively.
The results show 370.4 times reduction of wear rate due to application of Expanite treatment. During the test, the coefficient of friction (CoF) was also measured.
The treated sample showed an increase of around 18%, this could be attributed to the change in wear mechanisms where the adhesive wear of soft untreated sample is replaced with an abrasive wear of the 100Cr6 test ball in the test pair with the treated sample. The CoF, wear volume and specific wear rate results are summarised in Table 1.
Table 1.: Mean wear rates measured on wear tracks.
| Hardening process | Coefficient of Friction | Counterface Wear Scar Volume (mm3) | Specific wear rate (mm 3/N.m) | Specific wear rate reduction |
|---|---|---|---|---|
|
Untreated
|
0,51
|
0,2537
|
1,0E-03
|
|
|
ExpaniteHard-Ti®30
|
0,60
|
0,0007
|
2,7E-06
|
370.4 times
|
