JPH0911200A - Surface erosion method for superalloy using liquid jet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method improved to realize the surface roughness of a super alloy of such a level as to avoid grit inclusion. SOLUTION: A base material surface roughing method includes a stage of preliminarily roughing across the surface of base material by grit blasting, a stage of preparing liquid jet of at least 192 MPa (28ksi), and a stage of moving liquid jet across the base surface while scanning the surface at the speed of feeding liquid to the surface in a quantity range from 0.7kg/cm<2> to about 5.5kg/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for coating a superalloy with a thermal spray coating,
In particular, it relates to a method of conditioning the surface of a superalloy to allow a thermal spray coating to adhere firmly to the surface of the superalloy.

[0002]

BACKGROUND OF THE INVENTION Generally, metal substrates to be coated by a thermal spray coating process are first roughened by grit blasting to achieve a surface roughness that allows good mechanical bonding. Grit blast, by its very nature, leaves grit inclusions in the substrate. The grit material is
For most applications it will consist of angular aluminum particles, although it may also contain silicon carbide and iron particles. Silicon carbide is no longer used in the grit blasting of heat resistant superalloys due to the consideration of forming a low melting phase that can adversely affect stress / rupture life. Today, virtually all grit blasting is done using alumina particles. The term "superalloy" includes cobalt, iron, titanium and nickel based alloys that exhibit both high strength and hardness levels.

For some applications, grit inclusions present a problem. The interface specification between the superalloy substrate and the coating limits the amount of intervening grit. Turbine blade coatings for use in aircraft engines must meet very tight interface inclusion limits. Therefore, the prior art had to meet grit inclusion limits while still achieving the desired level of surface roughness to ensure adherence to subsequently coated coatings.

Superalloy surfaces must exhibit the proper surface roughness to achieve a well bonded thermal spray coating, but at the same time the surface must be clean. Therefore, fats and surface oxides that may be present from previous pretreatments should be avoided. The prior art has achieved a clean substrate through the use of a wet abrasive cleaning process, which also adds fine grit inclusions to the superalloy surface. Since the wet abrasive cleaning process is followed by the dry grit blasting process, the combination of both added significant amounts of inclusions, ie up to 15% of the interface level. It has been found that the presence of alumina inclusions at the otherwise clean interface allows the reaction to occur during subsequent heat treatment, resulting in undesired interfacial discoloration.

[0005]

The object of the present invention is to provide an improved method for achieving a certain level of superalloy surface roughness such that grit inclusions are avoided.

[0006]

A liquid jet is used to roughen the surface of a substrate so that the subsequently coated thermal spray coating material can adhere to the surface. The substrate is preferably a nickel or cobalt based superalloy. The method prepares a high pressure liquid jet and at least about 0.7 kg / c.
The liquid jet is moved while scanning across the substrate surface at a rate such that liquid is delivered to the surface in the volume range of m ² to about 5.5 kg / cm ² . The high pressure liquid jet is preferably about 192 MPa (28 ksi) to 357.
Provided from a reservoir maintained at a pressure in the range of MPa (52 ksi). A preferred embodiment preliminarily uses an initial blast of grit on the surface of the substrate to roughen a smooth finished surface from the substrate prior to application of the liquid jet. The initial grit blast allows the pressure and amount of applied liquid to be reduced to achieve the desired range of surface roughening.

[0007]

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, a high pressure water jet is used to roughen the surface of a superalloy in preparation for subsequent thermal spray coating. The purpose is to reduce the minimal amount of interfacial inclusions generated on the superalloy surface from the roughening stage. In many waterjet applications such as metal and ceramic cutting and cutting, abrasives are added to high pressure waterjets and significantly enhance their cutting speed. The present invention does not use abrasives in the water jet, only pure liquid that has been filtered and clarified by reverse osmosis.

As is apparent from the data below, a super alloy (or other metal) with pure water jets exhibiting a given pressure with little to no surface inclusions that would adversely affect the subsequently sprayed coating. ) Was confirmed to give sufficient surface erosion. In addition to allowing surface erosion, the jet of water jets also provides a cleaning action on the substrate surface.

The main findings of the present invention are as follows: A critical minimum or threshold water jet pressure is required to attack superalloys and other seed metals. The minimum or threshold water jet pressure varies with substrate hardness. 2. A minimum amount of water (or other seed liquid) must be delivered to cause measurable erosion of the substrate. No appreciable erosion will occur until the minimum amount of water has been delivered. The period until the start of erosion is called the "latency period". 3. It has been found that a light grit blast pretreatment to remove the finished surface of the substrate substantially enhances the subsequent waterjet erosion. A light grit blast pretreatment eliminates the latency period, allows the use of lower pressure waterjets and reduces the minimum waterjet pressure to achieve the desired level of erosion.

A useful range for waterjet erosion of a substrate is when a sufficient level of roughness is obtained with minimal substrate removal. The minimum roughness required for a thermal spray coating is about 0.02 mm (80 μin),
And a super alloy (ie IN-718)
About 5 mg / cm ² (about 0.006 mm of base material)
(1/4 mil) thickness is eliminated.
The maximum roughness for the subsequent thermal spray coating is about 0.13 mm (500 μin) due to the self-shielding and hiding effects of the thermal spray coating, and thus incomplete coverage at the interface and reduced bond strength.

In order to achieve sufficient surface roughening, the average minimum strip thickness was found to be about 0.005 mm (0.2 mil). This corresponds to a deletion amount of about 4.5 mg / cm ² for a typical superalloy surface.
The maximum acceptable removal thickness is about 0.05 mm (2 mils). This limitation is based on consideration of the reduced cross section of thin wall superalloys used for turbine blades. This removal thickness is about 45 mg / cm of the substrate surface.
Corresponds to erosion of ² . In addition, a sufficient and useful roughness for subsequent thermal spray coatings is about 0.041 mm (1
60 μ inches) and in IN-718,
Obtained at an erosion rate of 10 mg / cm ² .

In order to achieve a suitable roughened superalloy surface for subsequent thermal spray coatings, the preferred ranges of roughness, erosion and thickness loss are as follows: Roughness: 0.013- 0.13 mm (50-500 μinch), Erosion amount: 4.5-45 mg / cm ² , Thickness loss: 0.006-0.051 mm (0.25-0.25)
2.0 mils).

The more preferable ranges of roughness, erosion amount and thickness loss are as follows: Roughness: 0.02 to 0.0501 mm (80 to 200 μ)
Inch), erosion amount: 5-20 mg / cm ² , thickness loss: 0.006-0.025 mm (0.25-0.25)
1.0 mil).

The above range can be achieved by the application of a pure water jet which is scanned across the surface in a raster fashion. The water jet must exhibit a pressure that is at least above a certain minimum (threshold) pressure for the alloy being roughened. Furthermore, the water jet scanning speed is set so that the amount of water applied per unit area is higher than the critical delivery.

Pretreatment with a light grit blast applied to the surface is followed by the application of a water jet.
It has been found that having lower water jet pressures allows for more rapid surface roughening.

As is apparent from the following data, in the present invention, the following IN-718, MAR-M509 and REN were used.
Both nickel-based and cobalt-based superalloys, referred to by the E80 trade name, were tested.
The composition of each of these alloys is as follows (wt%): (IN-718) carbon: 0.05 chromium: 19 aluminum: 0.5 titanium: 1.0 molybdenum: 3.0 niobium: 5.0 Zirconium: 0.01 Boron: 0.005 Iron: 18 Nickel: balance (MAR-M509) Carbon: 0.55-0.65 Chromium: 21.0-24.0 Nickel: 9.0-11.0 Tungsten: 6.5-7.5 Tantalum: 3.0-4.0 Titanium: 0.15-0.25 Zirconium: 0.40-0.60 Manganese: 0.10max Silicon: 0.40max Boron: 0.01max Iron : 1.50max Sulfur: 0.015max Cobalt: Balance (RENE80) Cobalt: 9.5 Chromium: 14 Molybdenum: 4 Tungsten: 4 Titanium: 5 Aluminum: 3 charcoal : 0.17 zirconium: 0.03 boron: 0.015 Nickel: the balance

[0017]

[Example] Flow International Model 9X pressu capable of generating maximum water pressure of 358 MPa (52 ksi)
The test was performed using a re Intensifire (intensifier). The water jet was formed by a 0.46 mm (0.016 inch) diameter sapphire orifice and the stream was scanned across the test substrate at various traverse speeds. However, in all cases, 0.76 mm (0.03 mm) between the scanning paths.
Inch) Commonly shifted. The distance between the jet outlet nozzle and the surface of the substrate was set to 7.6 cm (3 inches). This is because it has been found to be the distance at which the maximum erosive action can be exerted.

The trace of one erosion scanning path is about 1.5 mm
It had a width of (0.06 inches). The alloy substrates were weighed before and after waterjet exposure and their thickness was measured. The amount of erosion was calculated as the mass of material removed (mg) per unit surface area (cm ² ). Most of the samples are 2
Although the button was a circular button having a diameter of 5.4 mm and a thickness of 3.2 mm, a part of the button was a size of a half-cut piece cut out from the root of the turbine blade or the sheet stock. The high pressure pump had the following flow rate through a 0.4 mm orifice: reservoir pressure 207 MPa (30 k
si), 276 MPa (40 ksi) and 345 MPa
At (50 ksi), 3.49 l / min, 3.
97 l / min and 4.50 l / min. From these flow rates and scan rates, the amount of water delivered to each sample was calculated in kg / cm ² .

Initial investigations of the effects of high pressure jets on various alloy coupons were conducted at 345 MPa (50 ksi) reservoir pressure and 30.5 cm / min transverse velocity. Based on these results, and in other homogenous specimens, tests were carried out at faster or slower traverse rates than before depending on whether the initial erosion loss was relatively large or small. These multipoint data are shown in the drawing.

The IN-718 specimen was 954 ° C (1750 °).
Solution annealed in F) for 1 hour and had a Rockwell B hardness of 103. The MAR-M509 coupon was as cast and had a surface Rockwell C hardness of 31.0. RENE 80 coupons were transversely cut from unidirectional solid solution rods that were standard solution annealed at 1200 ° C. for 4 hours in vacuum and had a final hardness of 39.4 HRc.
The initial MAR-M509 coupon surface was polished and post-vibration finished using triangular aluminum media dispersed in water. The RENE80 test piece was polished to a finish of 0.3 μm. The eroded surface was examined with a scanning electron microscope and roughness was measured using a hand-held Taylor-Hobson roughness meter set at a 0.73 mm (0.03 inch) cutoff.

FIG. 1 is a plot of the relationship between the amount of supplied water (kg / cm ² ) and the amount of corroded metal (mg / cm ² ) with respect to IN-718. Two important features of the waterjet erosion process are apparent from the graph of Figure 1. One is that there is a minimum amount of water needed to impact the IN-718 substrate before there is measurable erosion, ie there is a latency period.
That is, at 276 MPa (40 ksi),
No substantial erosion occurs until 0.8 kg / cm ² of water has been delivered across the substrate. At that point erosion begins and grows exponentially. 345 MPa (50
In ksi), the incubation period is about 0.5 kg / cm ²
Ends in.

The second feature is that there is a minimum (threshold) pressure required to cause measurable erosion and 207
MPa (30 ksi) is only slightly above the minimum pressure. The minimum erosion pressure can be determined from the first slope of the curve. Solution annealing IN-
The minimum pressure for 718 is about 196 MPa (28.5 k
si) was confirmed. From Bernoulli's formula,
The minimum pressure can be converted to a water jet velocity, thus the corresponding minimum velocity for IN-718 is 650 m / sec.

In FIG. 2, 954 ° C. (1750 ° F.)
Solution annealed for 1 hour at 718 ° C (1325 ° C)
A similar erosion test was performed on the aged IN-718 specimen that had been aged at F) for 8 hours at + 621 ° C (1150 ° F) for 10 hours. The aged IN-718 coupon had a Rockwell B hardness of 115. It should be noted that the amount of metal erosion is much lower than that shown in FIG. 1, demonstrating a clear dependence on substrate hardness.

The experiment shown in FIG. 1 was repeated on an IN-718 coupon that had been pretreated with a light grit blast to roughen the initial smooth finished surface of the coupon (FIG. 3). 9 pieces of 240 mesh square alumina grit
It was projected using a blast head located 5.1 cm (2 inches) from the specimen at a 0 degree impact angle. Projection grit pressure is 2.5 kg / cm ² gauge pressure (35 psig)
Met. Subsequent to grit blasting pretreatment, the specimen pressure was 207MPa (30ksi), 276MP
Placed under waterjet erosion test at a (40 ksi) and 345 MPa (50 ksi). It should be noted that in each case there is a considerable increase in the amount of metal erosion at each waterjet pressure.

In FIG. 4, erosion of a grit blasted and post waterjet roughened sample and a portion of the same sample that was not subjected to the initial grit blast and was waterjet roughened. Plots showing the direct comparison of the values are shown. In the plot of FIG. 4, the amount of erosion is plotted against the waterjet pressure, and the erosion starts at a much lower pressure when the sample is grit blasted and handplate compared to when not. It should be noted that

In FIG. 5, the amount of water delivered to the substrate is plotted against erosion weight loss for some materials subjected to a water jet roughening process of 345 MPa (50 ksi). The IN-718 coupon data described above (1 hour solution annealing at 954 ° C (1750 ° F)) was plotted and over solution treated (954 ° C (175 ° C).
Data was added for IN-718 specimens at 0 ° F) for 4 hours) and Ti-6 wt% Al-4.
Data for the wt% V sample is also added. This titanium alloy is IN-718 (954 ° C (1750 °
F) showed somewhat similar behavior to solution annealing for 1 hour), but IN-718 (4 hours at 954 ° C (1750 ° F)) was much higher for the equivalent amount of water delivered. It was erodible. As can be seen from the data plotted in Figure 5, there is a considerable difference in the erosion weight loss achieved in the IN-718 sample depending on the heat treatment condition. For the case of water jet erosion at 345 MPa (50 ksi), a weight loss of 40 mg / cm ² was 7.5 μm for IN-718 (1 hour solution annealing at 954 ° C. (1750 ° F.)). A roughness of 11.5 μm was achieved for IN-718 (4 hours at 954 ° C. (1750 ° F.)). At the same jet pressure and feed rate, the over-solutionized material had substantially higher erosion loss and greater roughness.

M as a function of the amount of water delivered to the substrate
The change in the amount of erosion of AR-M509 is shown in FIG. 35
The 9 MPa (52 ksi) erosion data curve increases exponentially with increasing feedwater collisions. 276 MPa (4
At 0 ksi), a similar, still exponential curve is seen, but both curves suggest that there is a latency period in the early stages of erosion.

In FIG. 7, the erosion status of RENE 80 is shown as a plot of erosion weight loss vs. water delivery. Note that it is clearly seen that there is a minimum of about 1 kg / cm ² before measurable erosion occurs.

The roughness of the eroded RENE 80 coupon is shown in FIG. 8 as a function of erosion weight loss. The roughness rises sharply with erosion and later moves towards a limit of about 30 μm at very high erosion weight loss. 220 mg / c
A weight loss of m ² corresponds to a surface removal of 0.27 mm (10.6 mils). This is substantially more than surface removal as needed to prepare for thermal spraying. However, 10 mg
At a weight loss of / cm ² , a roughness of about 5 μm resulted, which was found to be very suitable for subsequent thermal spray coatings.

In FIG. 9, the results of the water jet erosion test are shown for steels having Rockwell C hardnesses of 40, 50 and 60. Again, it should be noted that the erosion weight loss depends essentially on the hardness of the substrate as well as the applied water jet pressure and feed water.

Suitable waterjets hitherto found in nickel-based superalloy turbine blades have been found to demonstrate that substrates that have undergone a waterjet roughening process provide a good substrate for plasma spray coatings. The parameters were used to clean and roughen in one step. The blade initially had a dark surface oxide, but the oxide was completely removed by the waterjet roughening process. Blade erosion loss is 10.7 mg / cm ²
Which corresponded to a thickness removal of about 0.012 mm. The blades were then coated with MCrAlY (where M is nickel, cobalt or iron) by argon-enclosed plasma spraying, heat treated in vacuum and finished and peened. Excellent bonding was obtained and the interface was completely clean in all areas.

The above results show that each of the substrate materials tested has a minimum pressure below which surface erosion does not begin. In Figure 10, a plot of minimum pressure versus hardness (Rockwell B) is shown for the three main superalloys tested, IN-718, MAR-M509 and RENE80. It should be noted that the minimum pressure increases exponentially with increasing hardness.

In FIG. 11, the amount of water delivered to both cobalt-based and nickel-based superalloys is plotted against waterjet water pressure. In each case, the water supply was 4.5 mg / cm2 of the base material.
It was what was needed to achieve the ^two . The amount of water supplied is 357 MPa for cobalt-based superalloy.
0.7 kg / cm ^{2 at} (52 ksi) to about 5.5 kg at 216 MPa (31.5 ksi)
Fluctuated up to / cm ² . In contrast, nickel-based superalloys require less water to achieve a similar erosion state, requiring less than 276 MPa (40 ks).
In i) there was a lower water jet pressure of approximately 1.5 kg / cm ² .

In summary, the tests described above show that there is a minimum waterjet pressure for each substrate material below which erosion does not occur. The pressures are shown below: (Minimum pressure) MAR-M509: 210 MPa (30.6 ksi) RENE-80: 248 MPa (36.2 ksi) IN-718: 196 MPa (28.5 ksi)

The following Table 1 shows the critical water amounts required to achieve the stated erosion levels on the various substrates tested. Each listed in Table 1 establishes the amount of water required at the indicated pressure for a minimum erosion level of 4.5 mg / cm ² . Also, 45 mg / c
The amount of water required to achieve the maximum erosion level of m ² is also shown (except one). The items in Table 5 marked with * are the interpolated values of the experimentally confirmed values.

[0036]

[Table 1]

While the above has been based on the use of water as a source of jet erosion, those skilled in the art will appreciate that the use of other pure liquids can be substituted. Examples of such liquids include ethylene glycol, high density alcohols, polywater and the like.

[0038]

EFFECTS OF THE INVENTION A predetermined level of surface roughness of superalloy is realized so that grit inclusions are avoided.

While the invention has been illustrated above, it should be noted that many modifications can be made within the spirit of the invention.

[Brief description of the drawings]

1 is a reservoir pressure of 207 MPa (30 ksi), 2
76 MPa (40 ksi) and 345 MPa (50 ks)
In i), it is a graph which shows the relationship of the amount of metal corrosion which shows the erosion situation of IN718, and the amount of water supply.

FIG. 2 Reservoir pressure 207 MPa (30 ksi), 2
76 MPa (40 ksi) and 345 MPa (50 ks)
In i), it is a graph which shows the relationship of the amount of metal corrosion which shows the corrosion condition of IN718 which carried out the aging process, and the amount of water supplies.

FIG. 3 Reservoir pressure 207 MPa (30 ksi), 2
76 MPa (40 ksi) and 345 MPa (50 ks)
In i), it is a graph which shows the relationship of the metal erosion amount which shows the erosion situation of IN718 which carried out the grit blast process, and the water supply amount.

FIG. 4 is a graph showing the relationship between metal erosion rate and water jet pressure showing a comparison between a grit blasted surface and an ungrit blasted surface for IN718.

FIG. 5 is a graph showing the relationship between erosion weight loss and feed water volume for some superalloys from a reservoir maintained at 345 MPa (50 ksi).

FIG. 6 is 221 MPa (32 ksi) and 276 MPa.
It is a graph which shows the relationship of the erosion weight loss with respect to MAR-M509 vs. amount of water supply from a reserver maintained at (40 ksi) and 359 MPa (52 ksi).

FIG. 7: 276 MPa (40 ksi) and 345 MPa
Renesas maintained at (50 ksi) to RENE80
5 is a graph showing the relationship between the erosion weight loss and the amount of supplied water.

8 is a graph showing the relationship of surface roughness versus erosion weight loss for RENE 80 under the conditions shown in FIG. 7.

FIG. 9 is a graph showing the relationship between erosion weight loss and feed water amount for three types of steel by water jet from a reservoir maintained at 345 MPa (50 ksi).

FIG. 10: IN-718, MAR-M509 and REN
FIG. 6 is a graph showing the minimum pressure vs. hardness relationship for achieving initial erosion for E80.

FIG. 11 is a graph showing the relationship between the feed water amount and the water pressure for achieving 4.5 mg / cm ² erosion for both cobalt-based superalloy and nickel-based superalloy.

Claims (7)

[Claims] 1. A method comprising: a. Pre-roughening by grit blasting across the surface of the substrate; b. Providing a liquid jet of at least 192 MPa (28 ksi), c. 0.7kg / cm ² to about 5.5kg / c
moving the jet of liquid across the surface of the substrate at a rate such that liquid is delivered to the surface in a volume range up to m ² . 2. Metal using a thermal spray coating device,
The method of claim 1 further comprising depositing a layer of ceramic or cermet material. 3. The jet pressure and the amount of liquid fed to the surface are 0.013 to 0.13 mm (50 to 500 μm) on the surface.
The method of claim 1 adjusted to roughen the surface within the inch range. 4. The method of claim 1 wherein the jet pressure and the amount of liquid delivered to the surface are adjusted to erode the surface to a thickness loss of no more than 0.05 mm (2 mils). 5. The method of claim 1 wherein the substrate is a superalloy selected from the group consisting of nickel based, cobalt based, iron based and titanium based alloys. 6. The method of claim 1 wherein the liquid jet is a superalloy selected from the group consisting of water, ethylene glycol, alcohols and polywater. 7. The thermal spray coating device comprises plasma spraying,
The method of claim 2 which is a superalloy selected from the group consisting of detonation guns, fast oxygen-fuel and fast bombardment systems.