a Manufacturing Engineering Center, Cardiff University, Cardiff, CF24 - - PowerPoint PPT Presentation

R.M. Mineva, M. Ilievab, J. Kettlea, G. Laleva, S.S. Dimova, I. Dermendjievb, R. Shishkovb

aManufacturing Engineering Center, Cardiff University, Cardiff, CF24 3AA, UK bDepartment of Materials Science and Technology, Rousse University, Bulgaria 1

PVD coating experiment Sample characterization FIB milling of the Cr/C coating Conclusions Motivation

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Hard coatings: CrC, CrN, CrN(C), TiN, TiC, TiN(C) (N atoms might be replaced by C) Complex of extreme properties useful for (µ µ µ µ)tooling:

• hardness,
• wear resistance,
• scratch resistance,
• corrosion resistance’
• low adhesion to the glass, polymers or metals.

Motivation master metal

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Concurrent material (CrC) and process (FIB) optimisation Motivation

Cleaning temperature Tc=500oC Time of cleaning tc=10 min The Ar gas flow rate (standard cubic centimetres per minute) GAr=28.6 sccm Pressure in the vacuum chamber during the cleaning Pc=15 Pa Pressure during the deposition of coating Pd = 0.45 Pa Temperature during the deposition Td = 450oC Time for deposition td=120 min The Ar gas flow rate GAr=11.4 sccm The CH4 gas flow rate GCH4=7 sccm Discharge voltage U=460V Discharge current I=7A Distance between the target and substrate Lt-s=70 mm Table 1 Ion etching and coating conditions

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PVD coating experiment

1500 1700 1900 2100 2300 2500 2700 2900 3100 3300 3500 40 50 60 70 80 90 2Θ° I Cr7C3 [321] Cr7C3 [102] Cr7C3 [421] Fe [110] Cr7C3 [312] Cr7C3 [801] Fe [200]

Fig.1 X ray diffraction patterns of Cr/C coatings onto the tool steel substrate.

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Sample characterization

Fig.2 DIC (differential interference contrast) picture

• f the CrC coating onto D2 tool steel.

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Sample characterization CrC

• Fig. 3 Stages of the TEM Lamellae preparation using FIB

in both milling and deposition mode and subsequent nano-manipulation of the prepared lamellae (x3500).

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Sample characterization

• Fig. 4 STEM image
• f the CrC lamellae.
• Fig. 5 Grain size distribution
• f the Cr/C coating.

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Sample characterization

Fig.6 FIB milled patterns produced with different ion beam current (Iion ) and time (ts). Number of layers NL=1

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FIB milling of the Cr/C coating

The ion fluence in nC/µm2 : where: Iion, nA - the target ion beam current of charged Ga+ ions; A, µm2 - the target area size of features.

A t I f

s ion i

× =

(i) High milling rates (>1 µm3/min): Iion > 1 nA; ts > 60 s; fi > 2.3 nC/µm2; (ii) Best surface quality: Iion =0.1- 0.5 nA; ts = 30-300 s; fi = 0.4- 0.5 nC/µm2; (iii) Compromise between (i)&(ii): Iion ∼0.5 nA; ts = 30-300 s; fi ∼ 0.9 nC/µm2

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FIB milling of the Cr/C coating

• Fig. 7 Depth of FIB milling as a function of Iion and ts.

(on x-axis: FIB current according to the legend)

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FIB milling of the Cr/C coating

20 40 60 80 4.7 2.3 2.3 1.9 0.9 0.9 0.9 0.5 0.4 0.4 Fluence, nC/µm^2 SD

• Fig. 8 Depth of FIB milling

as a function of fi.

• Fig. 9 The influence of fi
• n surface quality.

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FIB milling of the Cr/C coating

1 2 3 4 5

4.7 2.3 2.3 1.9 0.9 0.9 0.9 0.5 0.4 0.4

Fluence, nC/µm^2 Depth, µm

5 10 15 20 25 30 35 5 10 15 20 25 30 35 40 45 Number of loops Surface Roughness, ra Fluence 1 Fluence 2

Fig.10 FIB milled CrC Iion =200mA, ts =120s, NL=1 (a) NL=50 (b).

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FIB milling of the Cr/C coating

reduced dwelling time:

• selective sputtering
• local redeposition

Ra (measured by AFM) as a function of NL

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Amorphous and polycrystalline Ni workpiece for performing FIB milling

PVD coatings were produced in thicknesses of about 30µm suitable for micro functionalisation of the surface. The stoichiometric composition of the coating material was x-ray determined to be Cr7C3. The properties of the nano structured (10nm average grain size) surface layers demonstrated good mechanical properties (MHV0.025 = 1400), superb corrosion resistance and good adhesion (measured by scratch tests). The experiments showed that to achieve a good surface finish with sputtering rates of approximately 1 µm3/min the FIB milling of the CrC coatings should be carried out with ion fluence of around 0.9 nC/µm2 . The best processing strategy is to use a higher number of layers in order to reduce the re-depositioning effect and improve the surface quality. Conclusions

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