5.5.1 Effect of post-treatment on microhardness of coated cemented carbide inserts Vickers microhardness test was performed on the AlTiN and TiAlN/AlCrN coated cemented carbide inserts with both as deposited as well as post treated conditions so as obtain their composite hardness. For each sample five readings were taken so as to the compute exact values. The average obtained value hardness for both the coatings is shown in the Table 14 and Table 15 and their corresponding graphs are shown in Figure 27.
61 Table 14. Microhardness values for (1) as deposited, (2) post-treated samples with AlTiN and TiAlN/AlCrN
Figure 27. Graphs representing microhardness values variation for (1) as deposited, (2) post-treated samples having AlTiN and TiAlN/AlCrN coatings.
From the plotted graphs for the hardness value it was found that the post-treated samples shown some improvement in their composite hardness values as compared to as deposited samples in both type of coatings. The value of the post-treated samples had increased to 2619.4 and 2499.35 from 2562.775 and 2258.625 in case of TiAlN/AlCrN and AlTiN samples respectively. This is because micro abrasive blasting causes generation of residual stresses which in turn improves the hardness . It was also observed that the
Sample Number TiAlN/AlCrN coating (A) AlTiN coating (L)
1 2562.775 2258.625
2 2619.4 2499.35
62 TiAlN/AlCrN have higher composite hardness value under same load conditions as compared to AlTiN coating may be due dual structure of the coating.
5.5.2 Effect of pre-treatment and combined pre-treatment as well as post-treatment on diffraction pattern of coated cemented carbide inserts
The obtained values for composite hardness of pre-treated and combination of pre-treated as well as post-treated samples is shown in Table 15 and their corresponding graphs are represented in Figure 28.
Table 15. Obtained microhardness values for (1) as deposited, (3) pre-treated, (4) combined pre as well as post-treated samples with AlTiN and TiAlN/AlCrN coatings.
Sample Number TiAlN/AlCrN coating (A) AlTiN coating (L)
1 2562.775 2258.625
Figure 28. Graphs representing microhardness values variation for (1) as deposited, (3) pre-treated, (4) combined pre and post treated samples having AlTiN and TiAlN/AlCrN coatings.
63 From the obtained result it was found that the hardness value had shown variation as compared to as deposited samples. For pre-treated sample there is slight improvement in the value i.e. from 2562.775 and 2258.625 to 2697.575 and 2502.32 for TiAlN/AlCrN and AlTiN coatings respectively. And for sample 3 the value had increased significantly i.e. up to 2986.875 and 2863.975 for TiAlN/AlCrN and AlTiN coatings respectively. This improvement in hardness value of sample 3 was due to improved brittleness of the surface and good adhesion of the coating material to its substrate.
5.6 Machining performance evaluation
Micro blasting has significant effect on the physical as well as mechanical characteristics of AlTiN and TiAlN/AlCrN coated cemented carbide inserts. These effects were well examined by various tests that were conducted on the samples. However, in order to investigate the performance of surface treated cutting tools, machining operation i.e.
turning was performed on austenitic stainless steel 316L at various machining parameters.
5.6.1 Effect of post-treatment on cutting performance of coated cemented carbide inserts in terms of machinability characteristics
(I) Cutting force
Figure 28 shows the variation of cutting force as a function of machining duration during turning operation using AlTiN and TiAlN/AlCrN coated inserts with and without surface treatment. From the obtained graphs it was found that the force values are higher at low cutting velocities. The value of cutting force increases with increase in the machining duration except at some points. This variation was shown due to progressive wear of the tool at the rake and flank surfaces.
Figure 29. Variation of cutting force with machining duration for as deposited and post-treated AlTiN and TiAlN/AlCrN coated samples
On comparing the values of cutting force for post-treated and as deposited samples it was observed that the value is always less in the previous as compared to later. This was correlated to the less wear in case of post-treated tools. At low cutting velocity, post-treated tools were subjected to large cutting force as compared to higher velocities because of large friction between the tool and workpiece interface which in turn causes wear.
Similar trend was observed for both types of coatings. However, the values of cutting forces were less in case of dual layer TiAlN/AlCrN coated tools because of its high hardness value (II) Chip characteristics
During the machining operation i.e. turning the effect of micro blasting on PVD deposited AlTiN and TiAlN/AlCrN tools cutting performance in terms of chip characteristics was examined. The various chip characteristics that were examined includes chip macro morphology, chip nature and chip reduction coefficient. For both types of coating the post-treated tools yielded discontinuous chips similar to as deposited conditions. High value of depth of cut attributed to formation of this type of chips. Figure 30 represents the chip macro morphology at various cutting conditions.
65 Figure 30. Macro morphology of chips obtained using as deposited and post-treated AlTiN and
TiAlN/AlCrN coated samples during turning of AISI 316
66 Chips obtained from cutting of AlTiN coated tools had very less length as compared to cutting by TiAlN/AlCrN coated tools. However the chip curling was more in case of AlTiN coated samples. Chip curling during the machining operation is always associated with the stress state of the chip layer next to the cutter. On examining the chips at higher magnification (as shown in Figure 31) it was found that the chip serration spacing decrease at later stage of machining i.e. when tool begins to fail. Chips obtained by cutting from post-treated samples appeared to have large chip serration as compared to chips obtained by cutting from as deposited. This may be due to less tool wear of the post-treated samples which exhibit high hardness value.
Figure 31. Magnified images of chips for examining chip serration for (a) as deposited and (b) post-treated samples.
Chips obtained by cutting from post-treated samples appeared to have large chip serration as compared to chips obtained by cutting from as deposited coating. This may be due to less tool wear of the post-treated samples.
Chip reduction coefficient is a function of chip thickness and is given by ratio of chip thickness to uncut thickness. On comparing the chip reduction coefficient value for sample L2 and L1 it was found its value was generally less for sample L2 except at some points. This can be attributed to the fact that sample L2 had undergone less wear at the cutting edge because of its high hardness. Wear on the rake surface and coating removal at
67 lower cutting speeds due to high drag force changed the trend 6of variation of chip reduction coefficient with machining duration.
40 60 80 100 120 140 160 180 200 220 240 260
Figure 32. Variation of chip reduction coefficient with machining duration for as deposited (L1) and post-treated (L2) conditions
In case of dual layer coating, similar trend was obtained for chip reduction coefficient. However, at some points the chip relation coefficient value related to post-treated sample decreased because of contribution of localized coating removal on rake surface.
Figure 33. Variation of chip reduction coefficient with machining duration for as deposited (A1) and post-treated (A2) conditions
(III) Tool wear
Machining was performed with three levels of velocities in order to examine the tool wear at different intervals of time i.e. at 60 s, 120 s, 180 s and 240 s at constant value of feed (0.2 mm/rev) and depth of cut (1.5 mm). The growth of rake and flank wear for AlTiN and TiAlN/AlCrN coated tools at cutting velocity of 100 m/min, 130 m/min, and 180 m/min are shown in Figure 34- Figure 36.
Figure 34. Growth of (a) rake and (b) flank wear of as deposited (L1, A1) and post-treated (L2, A2) samples with AlTiN and TiAlN/AlCrN coatings at V= 100 m/min.
Built up edge formation
Figure 35. Growth of (a) rake and (b) flank wear of as deposited (L1, A1) and post-treated (L2, A2) samples with AlTiN and TiAlN/AlCrN coatings at V= 130 m/min.
Figure 36. Growth of (a) rake and (b) flank wear of as deposited (L1, A1) and post-treated (L2, A2) samples with AlTiN and TiAlN/AlCrN coatings at V= 180 m/min.
72 The growth of wear at rake and flank surfaces can be easily examined with the help of the optical microscopic images. The wear of the tool is generally judged with by examining the flank wear values. A tool is said to be failed when the value of flank wear VB reaches 0.3 mm. So to examine tool wear analytically, graphs were plotted (shown in Figure 37 and Figure 38) for both types of coated samples at varying velocity
Figure 37. Variation of flank wear with machining duration in case of AlTiN coated tools with as deposited (L1) and post-treated (L2) conditions
Figure 38. Variation of flank wear with machining duration in case of TiAlN/AlCrN coated tools with as deposited (A1) and post-treated (A2) conditions
During the analysis it was found that post-treated sample had undergone less wear at the flank surface as compared to as deposited samples in both types of coatings. This was correlated to increased hardness value of the samples after post-treatment. However at some instances abnormal behaviour was observed for wear due to built-up edge formation. At cutting velocity of 100 m/min and time duration of 120 s, post-treated coated tools suffered
74 from removal of coating at selective locations resulting in formation of built up edge which was later removed by etching using sulfuric acid solution.
It was also observed that the dual layer TiAlN/AlCrN coated samples for both conditions had underdone less wear as compared to the multilayer AlTiN coated samples because of high hardness value of dual layer coated samples. After certain duration of time interval, the value of flank wear for TiAlN/AlCrN coated samples had increased rapidly and approximately same flank wear values were obtained in both the samples (i.e. in A1 and A2). Local substrate revelations at the cutting edge and flank surface caused by increased mechanical and thermal loads led to this type of behaviour of the coating which in turn decreased its cutting performance. Even though, the wear values obtained at 240 s for TiAlN/AlCrN samples were found to less as compared to AlTiN coated samples which had undergone gradual wear.
5.6.1 Effect of pre-treatment as well as combined pre-treatment and post-treatment on cutting performance of coated cemented carbide inserts in terms of machinability characteristics
(I) Cutting force
Variation of cutting force as a function of machining duration during turning operation using AlTiN and TiAlN/AlCrN coated inserts (with different conditions) is shown in Figure 39 and Figure 40. From the obtained graphs it was found that force showed an increasing trend with machining duration for all types of samples. However there was variation in the force value for each type of sample. Since as deposited sample underwent inhomogeneous wear at its cutting edge as well as its rake surface so friction value increased between tool and workpiece, thus results in higher application of force.
Figure 39. Variation of cutting force with machining duration for as deposited, pre-treated and combined pre as well as post treated AlTiN and TiAlN/AlCrN coated samples
But in case of pre-treated sample the wear was less as compared to as deposited because of high adhesion and low value of superficial surface roughness which in turn reduces the friction as well as cutting force between tribological pair i.e. tool and workpiece. The cutting force variation for pre-treated samples with machining duration were very much similar in both types of coating except its value. Cutting force value for pre-treated samples with TiAlN/AlCrN (A3) coating was less as compared to pre-treated samples with AlTiN coating (L3) due to its high strength and less wear.
The samples with combined pre-treatment as well as post-treatment have also shown similar trend as that of other two samples. Cutting force value obtained for the sample L4 was less as compared to L1 because prior micro abrasive blasting has increased adhesion strength of coating while the post blasting has increased it hardness. For sample A4 large value of force was very much similar to A1 at machining duration 240s. The variation in the force value at some points is due to removal of coating grains.
76 (II) Chip characteristics
During the machining operation i.e. turning the effect of micro blasting on PVD deposited AlTiN and TiAlN/AlCrN tools cutting performance in terms of chip characteristics was examined.
Figure 40 represents the chip quality and chip morphology for the chips obtained by using various cutting tools at start and end run of machining operation. From the study it was found that discontinuous chips was produced in all the cases. Though there was not much difference in the chip type but a significant difference in the chip quality in terms of chip length and chip curling was found for different types of samples.
Chips obtained by using pre-treated tool were larger in length and were having more curling as compared to chips from as deposited tool. There was an increase in chip curling with increased cutting velocity which in turn reduces the chip tool contact area (less chip tool contact area was obtained in pre-treated as well as combined pre-treated and post-treated samples.
V = 180 m/min
L1 L3 L4
Chip type Discontinuous Discontinuous Discontinuous
Chip type Discontinuous Discontinuous Discontinuous
77 Figure 40. Macro morphology of chips obtained using as deposited, pre-treated and combined pre as well as
post-treated AlTiN and TiAlN/AlCrN coated tools during turning
Figure 41 represents the chip cross-sections for chips obtained by using pre-treated tool (L3) and combined pre-treated as well as post treated tools (L4) which have difference in their chip segregation as compared to as chips obtained using as deposited tools.
Figure 41. Magnified images of chips for examining chip serration for (a) pre-treated and (b) combined pre as well as post-treated samples.
The trend obtained for variation of chip reduction with machining duration is shown in the Figure 42. From the plotted graph it was found that the chip reduction value for pre-treated as well combined pre-pre-treated and post-pre-treated was less as compared to as deposited
A1 A3 A4
Chip type Discontinuous Discontinuous/Snar
Chip quality Discontinuous Discontinuous Discontinuous
78 in both types of coatings except at some points. The trend obtained was due to the low friction offered by these samples as compared to as deposited which underwent high wear due to defamation of the coating material from the cutting edge.
40 60 80 100 120 140 160 180 200 220 240 260
Figure 42. . Variation of chip reduction coefficient with machining duration for as deposited (L1, A1), pre-treated (L3, A3) and combined pre as well as post pre-treated (L4, A4) conditions
(III) Tool wear
Machining performance of the tools in terms of tool wear was examined at higher cutting velocity value i.e. at 180 m/min at different intervals of time i.e. at 60 s, 120 s, 180 s and 240 s at constant value of feed (0.2 mm/rev) and depth of cut (1.5 mm). Figure 43 and Figure 44 represents growth of rake and flank wear of AlTiN and TiAlN/AlCrN coatings at cutting velocity of 180 m/min. On comparing the optical micrographs of the treated samples with as deposited samples for both the coatings it was found that pre-treated samples had shown less flank and rake wear compared to the as deposited coated tools. This improvement in performance of the pre-treated samples was due to improvement in the adhesion strength between the coating material and substrate due to the micro blasting.
Figure 43. Growth of (a) rake and (b) flank wear for as deposited, treated as well as combined pre-treated and post-pre-treated AlTiN coated tools with machining duration
Figure 44. Growth of (a) rake and (b) flank wear for as deposited, treated as well as combined pre-treated and post-pre-treated TiAlN/AlCrN coated tools with machining duration
81 These obtained results also shown correlation with the less values of the cutting forces in case of pre-treatment. Combined pre-treated as well as post-treated samples had undergone least wear in comparison with pre-treated, as deposited and post-treated samples in both types of coatings. This is due to improvement of the mechanical properties i.e.
adhesion, hardness, strength of the tool.
Variation in the flank wear for different samples can be examined analytically through the plotted graphs in Figure 45. In case of pre-treated AlTiN samples it was found that at initial stage flank wear was very much similar to as deposited condition. However at later stage pre-treated samples had shown less wear which resulted in improved tool life.
For combined pre-treated as well as post-treated samples the less wear can also be examined through the graphs obtained for both types of coating i.e. AlTiN and TiAlN/AlCrN.
40 60 80 100 120 140 160 180 200 220 240 260
Figure 45. Variation of flank wear with machining duration for as deposited and surface treated AlTiN and TiAlN/AlCrN coated samples
Conclusion. The Vickers Hardness test is easy to use, and its benefits far outweigh any potential disadvantages. The versatility of its use – the fact that it can be used to measure the hardness of almost any type of material – still makes it very attractive and widely applicable.How do you read a Vickers hardness test? ›
- The numeric hardness value (between 1 and 3000);
- The two letters "HV", standing for "Hardness according to Vickers";
- The applied test load in kgf;
- According to ISO 6507: The dwell time of the test load, but only if this is not between 10 and 15 seconds (uncommon in practice)
Vickers Pyramid Hardness Testing (DPH)
Although Vickers test method is different than Brinell, the scales are identical up to about a hardness of 300. The Vickers test is less prone to the errors produced by the Brinell system because a diamond square based pyramid is used, which does not deform as easily as a ball.
Rockwell B measures softer metals such as brasses. Rockwell C is used for harder metals such as steels. When conducting Rockwell Hardness tests most metals are tested several times, and the average hardness value as well as the standard deviation are reported.What does a high Vickers hardness number mean? ›
It is comprised of a diamond indenter and a light load to produce an indentation on the subject under testing. The depth of indentation is converted into the hardness value of the object. The smaller the indentation, the harder the object. Likewise, if the indentation is large, the material is lacking in hardness.What is the limitation of Vickers hardness test? ›
One limitation of the Vickers test is its speed. Most international test methods limit how fast the test can be performed so that repeatable results are obtained. Also, some kind of surface preparation is typically required so that the diagonal lengths required to calculate the area are clearly visible.How do you calculate microhardness? ›
In microhardness testing, an indentation is made on the specimen by a diamond indenter through the application of a load P (Figure 5.5). The size d of the resultant indentation is measured with the help of a calibrated optical microscope, and the hardness is evaluated as the mean stress applied underneath the indenter.How do you read data hardness? ›
Less than 60 mg/L is considered soft. Between 60 and 120 mg/L is considered medium hard. Between 120 and 180 mg/L is considered hard. More than 180 mg/L is considered very hard.What is the purpose of Vickers hardness test? ›
In most cases, the Vickers hardness test is used to determine hardness in materials in the micro hardness test load range. However, the Knoop hardness test is often used when hardness testing thin layers, such as coatings, or to overcome the problem of cracking in brittle materials.Why Vickers method of hardness testing is accurate compared to Rockwell method? ›
Vickers Hardness Test
It uses an even smaller diamond indenter than a Rockwell machine. The Vickers test has an optical system that enables magnification of the material's target area. This allows the tester to focus on microelements on the surface and provides a more accurate and pinpointed test.
Microhardness Testing is a method of determining a material's hardness or resistance to deformation when test samples are not suitable for macro-hardness. Microhardness testing is ideal for evaluating hardness of very small/thin samples, complex shapes, individual phases of a material, and surface coatings/platings.What is the main advantage of the Knoop hardness test over the Vickers microhardness test? ›
The Knoop method has the following advantages:
The test is non-destructive, and there is only very minor damage to the specimen surface (less than that with Vickers, because both the indentation depth and the risk of crack formation at the indent edge in glass and ceramics is lower than with Vickers).
60-62 HRC: The knives remain sharp for a long time but have more risk of becoming brittle. Harder to sharpen, and quality depends on the production. Mostly used in Japanese knives. 63-66 HRC: Needs cleaning after each use and more prone to breaking and becoming brittle.How hard is 50 HRC? ›
For example, the average axe has an HRC of about 50, so the sharpened edge can withstand the impact of being hurled into a solid piece of wood without snapping off. An HRC rating of 52-54 is soft but would make a reasonable, inexpensive kitchen knife.Is 58 Rockwell hard? ›
Hardness is a measure of a steel's resistance to deformation. Hardness in knife steels is most commonly measured using the Rockwell C test. Hardened knife steels are generally about 58/62 HRC (hardness Rockwell C), depending on the grade.Which standards define Vickers hardness test? ›
The hardness (HV) is expressed as, e.g., HV 10, for a 10 kg load, or HV 5 for a 5 kg load. Figure 9.14. Vickers hardness testing machine. Vickers hardness testing is carried out to standards such as ASTM E384 or ISO 6507 which has four parts describing the test itself, calibration and hardness tables.What are the uses of Vickers hardness test? ›
In most cases, the Vickers hardness test is used to determine hardness in materials in the micro hardness test load range. However, the Knoop hardness test is often used when hardness testing thin layers, such as coatings, or to overcome the problem of cracking in brittle materials.Why do we test hardness? ›
What is the definition of hardness testing? The application of hardness testing enables you to evaluate a material's properties, such as strength, ductility and wear resistance, and so helps you determine whether a material or material treatment is suitable for the purpose you require.Which type of material is used for the indenter? ›
Tungsten carbide is one of the least reactive indenter materials at high temperatures, which enables its application for high-temperature nanoindentation testing of metal alloys. In many ways, the material of the indenter tip must be diagnosed with some understanding of the material under test.What is Anvil effect? ›
For the indentation test on sheet metals, significant error can occur in measuring the penetration depth due to the anvil effect. This anvil effect is manifested with decreasing specimen thickness and increasing indentation depth.
Microhardness can synthetically display the elasticity, plasticity and strength of materials. On measuring the hardness distribution in the weld (Fig. 17.20), the result shows that softening takes place in a particular zone.Which indenter is used for microhardness test? ›
A Knoop indenter is used to press into a surface to measure hardness. The Knoop indenter, however, is shaped differently than a Vickers indenter for microhardness or a Berkovich indenter used in nanoindentation. The shape for the Knoop indenter is more elongated or rectangular.
Which standards define Vickers hardness test? Explanation: Vickers hardness test is defined by ASTM standard E92-72.What is unit of hardness? ›
The SI unit of hardness is N/mm². The unit Pascal is thus used for hardness as well but hardness must not be confused with pressure. The different types of hardness discussed above have different scales of measurement.What are types of hardness? ›
There are three main types of hardness measurements: scratch, indentation, and rebound. Within each of these classes of measurement there are individual measurement scales. For practical reasons conversion tables are used to convert between one scale and another.Which hardness test is more accurate? ›
The Rockwell test is generally easier to perform, and more accurate than other types of hardness testing methods.What determines material hardness? ›
Hardness is the ability of a material to resist deformation, which is determined by a standard test where the surface resistance to indentation is measured. The most commonly used hardness tests are defined by the shape or type of indent, the size, and the amount of load applied.What is the hardness value of steel? ›
➨ Modern steels of powder metallurgy rank highest on the Rockwell scale and boast hardness around 64 and 68 HRC.How is Rockwell hardness calculated? ›
Multiply scale factor, 500 , by depth of penetration, d . Subtract the product from the scale factor 100 to obtain the Rockwell hardness (HRC) number. Mathematically, that's: HRB = 100 - 500 × d .How many times can you anvil an item? ›
On average, you'll be able to use an anvil about 25 times before it's destroyed, but it can be much more or much less depending on how lucky you are.
Anvils themselves cannot be repaired. Using your anvil will cause your anvil to degrade, so try not to use the anvil unless you really want to. You will need to make a new anvil if your old anvil breaks.How do I make an anvil? ›
How to Make an Anvil in Minecraft Survival (Recipe Tutorial) - YouTube