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Coatings expert teaches hardmetal sinterers what nanosize really means
Coatings expert teaches hardmetal sinterers what nanosize really means ome hardmetal manufacturers think they've reached 'nanosize' with an average carbide grain size of 0.4 jam (400 nm). Others wait until they've reached 200, 100 or even 10 nm. Of course, none of these are truly nanosize - or 'nanocrystalline' any more than 10 jam particles (0.01 ram) are 'micron-sized.' Now the first 'superlattice'-type coatings are showing the sinterers what the terminology really
S
means. Sumitomo Electric's latest ZX coating {Figure 1) has no less than 2000 distinct layers averaging 1.25 nanometres in thickness, a total of just 2.5 micrometres for the multilayer stack (though not including a possible - but undisclosed - base coat or a final topcoat).
MPR
readers saw it coming
In the hardmetals industry, innovations tend to emerge quietly
Thickness 3 pm P about 1.5 larn x2ooo layers substrate
Figure1:ZXcoatingwithTiN/AIN superlattice (P = periodicity). Physical structure of
(hexagonal, cubic) Distance Bulk modulus Structure (nm) (GPa)
TiN, AIN
i normal
phase cubic a=0.424 i normal a=0.308 i phase hexagonal c=0.493 a=0.412" AIN i high pressure phase (oubic) (3.0%) I
TiN
Hardness (HV)
288
2000
200
1200
I
i
~ C u b i c
-329* ? * estimated
~hexagonal
Figure2: Formationof cubic aluminium nitride. 16
M PR April 2 o o l
oo26-o657/ol/$
and to take as long as ten years or even more - before they gain general acceptance. Such has been the case with grain-refined submicron grades, for diamond coatings and for many other technical developments. Superlattice coatings seem to be no exception. We first spotted the trend at the Plansee Seminar in May 1997, when we reported to Metal Powder Report readers (MPR, October 1997, p. 13), under the heading 'Superfine multilayer coatings' that: "An interesting paper, from a team representing Sandvik, Balzers and Uppsala University, demonstrated a new technique for PVD coating. In essence, the substrate holder is rotated above a much smaller electrode in an evacuated deposition chamber. As each insert or tool passes above the electrode, a very thin layer is deposited. Depending on coating deposition rate and speed of rotation, individual lamellar coatings can be held to a nanometric or superlattice scale, typically 30 and 150 nm for alternating Ti and TiN, for 10 and 60 seconds deposition time, respectively. Hardness was substantially enhanced, and good results were obtained in milling stainless steels with lamellar TiN/NbN-coated carbide. Turning operations with similar materials had not yet been tried." (Further details of these systems are provided in the article from Sandvik on pp. 24-30.) Later in the same year, we reported the following from EMO, the European Machine Tool Show (MPR December 1997, pp. 16-19): "Although few details have been given, Sumitomo's ZX 'superlattice'
- see f r o n t m a t t e r © 2 o r e Elsevier Science Ltd. All rights reserved.
Properties 5000
ZX coating
Sumitomo's ZX is the world's first 2000,ooo ].ayer coating, comprising alternate lay-1ers oftitanitmn nitride 3000 z TiN/AIN superlatlioe TiN and aluminium ¢nitride A[N. 'Bulk' ,a_ -r TiN has a cubic S u bstrate 20001~ TiN atomic strLicEirc with hardness of ~d~oul 2000 HV. W h e n I O00qAIIINI I I I I , r I , 1 k 1 I formed at low tem0 5 10 15 peratures, A1N has a Stacking period, P ( n m - ~ / l o o o gm l~exagona{ structure Cubic AI N: and hardness of only Coherent interface 1200 HV, but in the ZX coating it is constrained by ~he Figure 3: Relationship of hardness and stacking period ror TTN/AIN superlattice. 'superlatticc' effect to multilayered coating is claimed to evacuated deposition chamber. its high-temperature cubic struchave a hardness 'equal to that of Each time the insert comes ture (Figure 2). For a stacking cubic boron nirride'. If tale, this around, another thin (typically 'period' of 1.25 rim (Figure 3), the would be a substantial break- one to a few nanomerres) layer is effective hardness of the multilaythrough in cutting technology. The deposited. By having two differing er coating peaks at as much as indusu T could pe]haps cease its ancxles vvitlaill the clnnmber, of d ill 4000 HV, a haldness similar to lengthy and vastly expensive femnt sizes, alternating cthick and that c)f a solid cubic Nwon nitride search f¢)r an ecom)mic CBN coat- thin' layers of each composition compact, l~y conqparison, a col-~ing, since it might have no better could be deposited with each rota- ventional titanium nitride {TIN) performance than this new pr<:d- tion of the turntable and a large coating has a typical hardness ~( UCt. Tests have heel1 carried {)ut on number of alternating layers can 2200 HM tital~ium Larlx:nitridc solid milling and drilling tools with be deposited in a short time. A (TiCN) 2700 HV and tiLanium apparently exceEent resuks. Wave- series of anodes, arranged like the aluminium n i m d e (T~AlN) ~200 shaped high-rake indexable inserts spokes of a wheel, produce even HV. with the ZX coating, for WEM more, but much thinner, layers in In addition to this extreme and WFM milling cutters, have each rotation. hardness, ~he coated surface is also delivered outstanding pert0f When at least one of the com- exceptionally smooth, since discontinuities tend to be in differmance." ponent layers is thin enough, tee Akhough a little poetic [icence dominant crystal structure is car- enr places on each level and thus was applied to the hardness com- ried across the intervening layer to "average out' on the total thickness (Figure 4). Excepti~mal parison, this was indeed a true as a 'superlattice', adding strength hardness gives longer tool life superlattice coating, far more and stability. advanced than if, at described at die Plansee Seminar and, moreover, a regular commercial product. Though details of the manufacturing process are still not published, much more data on structure, properties and applications have now I~ecome available.
Manufacture Large-scale production of socalled 'superlatdce' coatings is by physical vapour deposition (PVD). This can be achieved by m o u n t ~ g the inserts to be coated on a turntable above an anode, or a series of anodes, within an
www.metal-powder.net
C o n v e n t i o n a l coating
New coating
Figure 4: Surface roughness of ZX coating compared with conventional coating.
MPR April 2 o o l
~7
Figure 5: SSM endmill with ZX coating for enhanced performance.
whilst the smoother surface improves the finish on machined workpieces. The basic ZX coating has a distinctive pinkish tinge, as seen on the Sumitomo SSM endmill of Figures 5 and 6a. A base layer of the same or differing composition absorbs intertZacial stresses and aids adhesion. This can typically be applied by
(C)
low-temperature chemical vapour deposition and would be thicker than any of the 'superlattice' layers. Adhesion strength of the latest ZX coating is said to be 100% better than that of a 'conventional' coating. A final, possibly thicker, topcoat can also be applied, to improve performance or appearance, or simply to confuse competitors. More recent Sumitomo cuttingtool coatings for inserts are understood to be of these types, and include Ace Coat ACZ310 for milling cast iron and Ace Coat ACZ350 (with a 'special, hightoughness' substrate) for milling stainless steel. The original ZX coating is intended mainly for solid
.....
I!i7
><
r
carbide tools, such as drills and endmills (Figure 6). W h a t don't w e k n o w ? Judging by the apparent dearth of competitive comparable products, Sumitomo either has very strong patents or has developed considerable know-how in a tricky area probably both. What we have seen lately from other companies have comparatively few and thicker layers, which Sumitomo say are far from optimum where properties and performance are concerned. So what are the possible variables? The coating chamber, assumed to be fi~r PVD, seems to be the key. Among the things we don't know are the size and shape of the chamber, the operating pressure, voltage and current, the arrangement of electrodes, and the layout and holding method of items to be coated. Do the items to be coated rotate, or the electrodes, or both, at what speed and on a vertical or horizontal axis? Are there different set-ups for coating endmills and indexable inserts? Is the underlying hardmetal FG (functional gradient) treated to enhance adhesion? Is there an underlying CVD layer for the same purpose? What topcoats are used, of what thickness, and are they applied by CVD, plasma CVD, PVD or some other method? We have noted that, no doubt for good reasons, available SEM photos of the super[attice coating (e.g. Figure 1 ) show only a central section and not the top surface or substrate/coating interface. We will be looking with considerable interest at this year's Plansee Seminar the first since 1997 (28 May - 1 June, Reutte, Austria), and at EMO in Hanover, Germany (12-19 September) for new scientific disclosures and new comraercial products involving superlattice coatings, both from Sumitomo and from their competitors. Look out for reports later in the year in MPR.
Figure 6: Applications of superlattice ZX coating. (a) High speed finishing with SSM ZX-coated endmil[; (b) ZX-coated wavemill inserts in action. (c) Range of MDS-K type multi-drills, ZX coated for high-speed drilling applications (d).
18
M P R April 2OOl
Kenneth J A Brookes (Consultant Editor)
www.metal-powder.net
S
means. Sumitomo Electric's latest ZX coating {Figure 1) has no less than 2000 distinct layers averaging 1.25 nanometres in thickness, a total of just 2.5 micrometres for the multilayer stack (though not including a possible - but undisclosed - base coat or a final topcoat).
MPR
readers saw it coming
In the hardmetals industry, innovations tend to emerge quietly
Thickness 3 pm P about 1.5 larn x2ooo layers substrate
Figure1:ZXcoatingwithTiN/AIN superlattice (P = periodicity). Physical structure of
(hexagonal, cubic) Distance Bulk modulus Structure (nm) (GPa)
TiN, AIN
i normal
phase cubic a=0.424 i normal a=0.308 i phase hexagonal c=0.493 a=0.412" AIN i high pressure phase (oubic) (3.0%) I
TiN
Hardness (HV)
288
2000
200
1200
I
i
~ C u b i c
-329* ? * estimated
~hexagonal
Figure2: Formationof cubic aluminium nitride. 16
M PR April 2 o o l
oo26-o657/ol/$
and to take as long as ten years or even more - before they gain general acceptance. Such has been the case with grain-refined submicron grades, for diamond coatings and for many other technical developments. Superlattice coatings seem to be no exception. We first spotted the trend at the Plansee Seminar in May 1997, when we reported to Metal Powder Report readers (MPR, October 1997, p. 13), under the heading 'Superfine multilayer coatings' that: "An interesting paper, from a team representing Sandvik, Balzers and Uppsala University, demonstrated a new technique for PVD coating. In essence, the substrate holder is rotated above a much smaller electrode in an evacuated deposition chamber. As each insert or tool passes above the electrode, a very thin layer is deposited. Depending on coating deposition rate and speed of rotation, individual lamellar coatings can be held to a nanometric or superlattice scale, typically 30 and 150 nm for alternating Ti and TiN, for 10 and 60 seconds deposition time, respectively. Hardness was substantially enhanced, and good results were obtained in milling stainless steels with lamellar TiN/NbN-coated carbide. Turning operations with similar materials had not yet been tried." (Further details of these systems are provided in the article from Sandvik on pp. 24-30.) Later in the same year, we reported the following from EMO, the European Machine Tool Show (MPR December 1997, pp. 16-19): "Although few details have been given, Sumitomo's ZX 'superlattice'
- see f r o n t m a t t e r © 2 o r e Elsevier Science Ltd. All rights reserved.
Properties 5000
ZX coating
Sumitomo's ZX is the world's first 2000,ooo ].ayer coating, comprising alternate lay-1ers oftitanitmn nitride 3000 z TiN/AIN superlatlioe TiN and aluminium ¢nitride A[N. 'Bulk' ,a_ -r TiN has a cubic S u bstrate 20001~ TiN atomic strLicEirc with hardness of ~d~oul 2000 HV. W h e n I O00qAIIINI I I I I , r I , 1 k 1 I formed at low tem0 5 10 15 peratures, A1N has a Stacking period, P ( n m - ~ / l o o o gm l~exagona{ structure Cubic AI N: and hardness of only Coherent interface 1200 HV, but in the ZX coating it is constrained by ~he Figure 3: Relationship of hardness and stacking period ror TTN/AIN superlattice. 'superlatticc' effect to multilayered coating is claimed to evacuated deposition chamber. its high-temperature cubic struchave a hardness 'equal to that of Each time the insert comes ture (Figure 2). For a stacking cubic boron nirride'. If tale, this around, another thin (typically 'period' of 1.25 rim (Figure 3), the would be a substantial break- one to a few nanomerres) layer is effective hardness of the multilaythrough in cutting technology. The deposited. By having two differing er coating peaks at as much as indusu T could pe]haps cease its ancxles vvitlaill the clnnmber, of d ill 4000 HV, a haldness similar to lengthy and vastly expensive femnt sizes, alternating cthick and that c)f a solid cubic Nwon nitride search f¢)r an ecom)mic CBN coat- thin' layers of each composition compact, l~y conqparison, a col-~ing, since it might have no better could be deposited with each rota- ventional titanium nitride {TIN) performance than this new pr<:d- tion of the turntable and a large coating has a typical hardness ~( UCt. Tests have heel1 carried {)ut on number of alternating layers can 2200 HM tital~ium Larlx:nitridc solid milling and drilling tools with be deposited in a short time. A (TiCN) 2700 HV and tiLanium apparently exceEent resuks. Wave- series of anodes, arranged like the aluminium n i m d e (T~AlN) ~200 shaped high-rake indexable inserts spokes of a wheel, produce even HV. with the ZX coating, for WEM more, but much thinner, layers in In addition to this extreme and WFM milling cutters, have each rotation. hardness, ~he coated surface is also delivered outstanding pert0f When at least one of the com- exceptionally smooth, since discontinuities tend to be in differmance." ponent layers is thin enough, tee Akhough a little poetic [icence dominant crystal structure is car- enr places on each level and thus was applied to the hardness com- ried across the intervening layer to "average out' on the total thickness (Figure 4). Excepti~mal parison, this was indeed a true as a 'superlattice', adding strength hardness gives longer tool life superlattice coating, far more and stability. advanced than if, at described at die Plansee Seminar and, moreover, a regular commercial product. Though details of the manufacturing process are still not published, much more data on structure, properties and applications have now I~ecome available.
Manufacture Large-scale production of socalled 'superlatdce' coatings is by physical vapour deposition (PVD). This can be achieved by m o u n t ~ g the inserts to be coated on a turntable above an anode, or a series of anodes, within an
www.metal-powder.net
C o n v e n t i o n a l coating
New coating
Figure 4: Surface roughness of ZX coating compared with conventional coating.
MPR April 2 o o l
~7
Figure 5: SSM endmill with ZX coating for enhanced performance.
whilst the smoother surface improves the finish on machined workpieces. The basic ZX coating has a distinctive pinkish tinge, as seen on the Sumitomo SSM endmill of Figures 5 and 6a. A base layer of the same or differing composition absorbs intertZacial stresses and aids adhesion. This can typically be applied by
(C)
low-temperature chemical vapour deposition and would be thicker than any of the 'superlattice' layers. Adhesion strength of the latest ZX coating is said to be 100% better than that of a 'conventional' coating. A final, possibly thicker, topcoat can also be applied, to improve performance or appearance, or simply to confuse competitors. More recent Sumitomo cuttingtool coatings for inserts are understood to be of these types, and include Ace Coat ACZ310 for milling cast iron and Ace Coat ACZ350 (with a 'special, hightoughness' substrate) for milling stainless steel. The original ZX coating is intended mainly for solid
.....
I!i7
><
r
carbide tools, such as drills and endmills (Figure 6). W h a t don't w e k n o w ? Judging by the apparent dearth of competitive comparable products, Sumitomo either has very strong patents or has developed considerable know-how in a tricky area probably both. What we have seen lately from other companies have comparatively few and thicker layers, which Sumitomo say are far from optimum where properties and performance are concerned. So what are the possible variables? The coating chamber, assumed to be fi~r PVD, seems to be the key. Among the things we don't know are the size and shape of the chamber, the operating pressure, voltage and current, the arrangement of electrodes, and the layout and holding method of items to be coated. Do the items to be coated rotate, or the electrodes, or both, at what speed and on a vertical or horizontal axis? Are there different set-ups for coating endmills and indexable inserts? Is the underlying hardmetal FG (functional gradient) treated to enhance adhesion? Is there an underlying CVD layer for the same purpose? What topcoats are used, of what thickness, and are they applied by CVD, plasma CVD, PVD or some other method? We have noted that, no doubt for good reasons, available SEM photos of the super[attice coating (e.g. Figure 1 ) show only a central section and not the top surface or substrate/coating interface. We will be looking with considerable interest at this year's Plansee Seminar the first since 1997 (28 May - 1 June, Reutte, Austria), and at EMO in Hanover, Germany (12-19 September) for new scientific disclosures and new comraercial products involving superlattice coatings, both from Sumitomo and from their competitors. Look out for reports later in the year in MPR.
Figure 6: Applications of superlattice ZX coating. (a) High speed finishing with SSM ZX-coated endmil[; (b) ZX-coated wavemill inserts in action. (c) Range of MDS-K type multi-drills, ZX coated for high-speed drilling applications (d).
18
M P R April 2OOl
Kenneth J A Brookes (Consultant Editor)
www.metal-powder.net